Osteichthyes


Text © Prof. Angelo Messina

 

Beltramini.gif
English translation by Mario Beltramini

 

Known as Bony fishes, the Osteichthyes are a class of vertebrates with jaws like this unyielding Tylosurus crocodilus.

Known as Bony fishes, the Osteichthyes are a class of vertebrates with jaws like this unyielding Tylosurus crocodilus © Jean-Marie Gradot

More commonly called Bony fishes, they represent a class of vertebrates equipped with jaws (Gnathostomata)  to which are attributed forms that characterize for having a completely ossified skeleton in the adult phase or anyway in a good part ossified, hence the scientific name of Osteichthyes.

In the most primitive forms, such as Placodermi and Ostracodermi, these fishes do not yet have the vertebral bones and the process of ossification affects only the skull that is covered by extensive dermal bones.

Only in the Teleostei the skeletal structures are completely ossified and the spinal column forms the support axis of the whole skeleton.

In the Osteichthyes, like in these loving Acanthostracion polygonium, the mouth opens in terminal position, unlike the Cartilaginous Fishes where usually it's ventral and oblique. The skull is formed by a variable number of bones that form a rigid box and their presence or absence has an important taxonomic value.

In the Osteichthyes, like in these loving Acanthostracion polygonium, the mouth opens in terminal position, unlike the Cartilaginous Fishes where usually it’s ventral and oblique. The skull is formed by a variable number of bones that form a rigid box and their presence or absence has an important taxonomic value © Allison & Carlos Estape

In this regard it is to be clarified that, traditionally deemed synonyms of Osteichthyes, presently with the term Teleostei is indicated a grouping that is located within the Actinopterygii, at a lower systemic level, that of infraclass.

It must be kept in mind that also in the Cartilaginous fishes (Chondrichthyes) the bony tissue is present but it is limited only to the minute placoid scales forming the dermal armours. Otherwise, in the Osteichthyes  the use of the bone tissue assumes a fundamental importance in the evolutionary developments of the class. As a matter of fact, during their evolutionary history, probably started in continental aquatic environments already since the most archaic forms, in the Bony fishes this tissue progressively replaces each cartilaginous component of the inner skeleton and of the dermal formations, from the cranial to the vertebral, branchial ones and of the fins.

Some Osteichthyes are very modest in size, like this Paedocypris progenetica who rarely approaches 10 mm.

Some Osteichthyes are very modest in size, like this Paedocypris progenetica who rarely approaches 10 mm © Ganjar Cahyadi

Typically the  Osteichthyes have the neurocranium formed by a varying number of bones arranged to form a rigid box. The presence or the absence of certain cranial bones assumes a remarkable meaning in their systematics.

Peculiarly, the mouth of the Bony fishes, in whose formation various ossified elements do participate, is usually wide and opens in terminal position, unlike the Cartilaginous fishes where it is usually ventral and oblique.

The jaws, usually well developed, are formed by ossified structures that articulate with the skull by means of a connection also bony. All the bony elements contributing to the formation of the mouth and even those forming the gill arcades may be equipped with teeth (pharyngeal mandible).

But on the other side, the Atlantic halibut (Hippoglossus hippoglossus) measures about 3 m.

But on the other side, the Atlantic halibut (Hippoglossus hippoglossus) measures about 3 m © Vsevolod Rudyi

The structural configuration of the mouth, particularly rich in skeletal elements, and its terminal position have allowed a series of adaptations of these fishes to the most varied dietary strategies of an extraordinary variety, characteristic standing at the base of the evolutionary success of the class.

The sizes of the Bony fishes are extremely varied, from a few millimetres to various metres. Among the smallest forms are to be surely mentioned the species of Paedocypris (Kottelat et alii, 2006), small fishes known for Sumatra waters who do not exceed 7.9 mm of length in the females and 10 mm in the males. Also the Dwarf pygmy goby (Pandaka pygmaea Herre, 1927) and the Sinarapan (Mistichthys luzonensis, Smith 1902), Gobiiformes of Philippines, respectively with 10 and 11 mm of length stand definitely among the smallest Bony fishes.

And the Swordfish (Xiphias gladius) is not less.

And the Swordfish (Xiphias gladius) is not less © Pierre Jaquet

Among the largest Osteichthyes appear the Swordfish (Xiphias gladius Linnaeus, 1758) and the Atlantic halibut (Hippoglossus hippoglossus Linnaeus, 1758), both almost 3 m long.

Among the giants of the class must surely be mentioned the Great sturgeon or Beluga (Huso huso Linnaeus, 1758) and the common Sturgeon (Acipenser sturio Linnaeus, 1758) who, albeit exceptionally, may reach the length of 6 metres.

The giants’ record undoubtedly belongs to the King of herrings (Regalecus glesne deep sea fish  Ascanius, 1772),  deep sea fish reported in the waters of all oceans that on average measures about 7 m but that it can reach and exceed even 10 m. In this regard, it should be remembered that until not too long ago in the Caspian Sea waters lived Sturgeons (Acipenser sturio Linnaeus, 1758) who did measure even 9 m weighing even a good 1500 kg.

Among the heavyweights the Ocean sunfish (Mola mola) stands out. It may weigh even one ton.

Among the heavyweights the Ocean sunfish (Mola mola) stands out. It may weigh even one ton © Giuseppe Mazza

However, apart from the few extremely sized forms, most Bony fishes usually measure less than 1 m. As a consequence, in relation to the dimensions, also the weight varies greatly and from a few grams it may reach even almost one ton, like in the Ocean sunfish (Mola mola Linnaeus, 1758).

Usually, the body of the Bony fishes is fusiform, however their appearance varies greatly. Many species of benthic, marine and of freshwater habits, have flattened bodies and in several groups, like in the eels, the same are elongated and serpentine.

Conversely, in some forms the body is globe-shaped, like in the Pufferfishes (Tetraodontidae), in others it is cubic, like in the Boxfishes (Ostraciidae) or also of singular shape, like in the surprising species inserted in the order of the   (Syngnathiformes)

In the puffer fishes like Arothron hispidus the body is globose and there is no lack of boxfishes like Acanthostracion polygonium in the photo above.

In the puffer fishes like Arothron hispidus the body is globose and there is no lack of boxfishes like Acanthostracion polygonium in the photo above © Giuseppe Mazza

The body of the Bony fishes is covered by ossified dermal scales (ctenoid, cycloid, at times ganoid). In some forms the body is protected by a real armour formed by ganoidian scales (Lepisosteiformes and Polypteriformes).

In some species the skin is completely bare or with few vestigial scales (Polyodontidae). Some species have the body partially bare and partially protected by bony plates or ganoid scales, like in the Sturgeons (Acipenseridae).

The body colouration is very varied and frequently is the most conspicuous character of the Bony fishes. The colouration is determined mainly by pigmented cells (chromatophores) located in the derma, outside the scales or under them, and whose number and disposition are controlled nervously or hormonally.

Very often the fishes may quickly change colour acting on the skin's chromatophores. It's the case for instance of this Hippocampus reidi.

Very often the fishes may quickly change colour acting on the skin’s chromatophores. It’s the case for instance of this Hippocampus reidi © Allison & Carlos Estape

In the members of the class, the eyes, usually lateral, have no eyelids and are usually well developed. Are present two dorsal olfactory sacs that do not communicate with the mouth cavity.

In the Osteichthyes the gills have a so-called comb-like shape due to the absence of septum between the respiratory lamellae. The gills are supported by four branchial arches and are arranged inside two branchial chambers, one per side, that communicate with the outside through appropriate openings placed behind the eyes. Gills and branchial chambers are protected by a fold of the integument sustained by opercular bones of dermal origin and that has relation with the hyoid arch.

Usually the Bony fishes completely lack spiracles and only in the species having more primitive characteristics this can be present, but in an extremely reduced form.

The fins, supported by several ossified dermal rays, arranged parallel to each other, like in this Acanthurus pyroferus, are typical of the Osteichthyes.

The fins, supported by several ossified dermal rays, arranged parallel to each other, like in this Acanthurus pyroferus, are typical of the Osteichthyes © Giuseppe Mazza

The members of this class have fins considerably differing in shape, dimensions and position. In most instances the fins are supported by several ossified dermal rays arranged parallel to each other.

Otherwise, the members of the Crossopterygii, a grouping of the Osteichthyes to which most scholars attributed the value of subclass, characterize for having each of the even fins, pectoral and pelvic, implanted in a single distinct  base that in turn articulates with the pectoral girdle and with the pelvic one.

From the bony parts of the fins of primitive OsteichthyesDipnoi or Crossopterygii, has most probably originated the skeleton of the.limbs of all Tetrapoda, vertebrates characterized by two pairs of limbs (Amphibians, Mammals, Reptiles, Birds) in some cases modified or disappeared during the evolution.

Anatomical element typical of Osteichthyes is also the swim bladder: an organ almost always hydrostatic but also breathing for the colonization of the subaerial environment, as it still happens today in the lost primitive forms. Absent where it is of no use, like in this Echeneis naucrates that mostly moves stuck to a host.

Anatomical element typical of the Osteichthyes is also the swim bladder: an organ almost always hydrostatic but also breathing for the colonization of the subaerial environment, as it still happens today in the lost primitive forms. Absent where it is of no use, like in this Echeneis naucrates that mostly moves stuck to a host © Allison & Carlos Estape

The tail of the Osteichthyes is typically homocercal or diphycercal, only occasionally heterocercal. Another anatomical element typical of the Osteichthyes is the presence of a swim bladder, an eversion of the wall of the alimentary tract, filled with gas that in most of these fishes is unique and placed dorsally to the digestive tract. In the most primitive forms (Dipnoi and Crossopterygii) this organ is instead formed by a pair of sac-shaped protrusions located in ventral position, behind the pharynx.

Throughout the history of the Osteichthyes, the swim bladder has undergone an evolutionary path that has developed along two directions guiding the evolution of these fishes, on one side towards a marked specialization for the aquatic environment and on the side towards the acquisition of characteristics, important premises for the colonization of the subaerial environment.

It is also absent in soles and in brills, species like this Bothus lunatus that live mainly resting on the seabed.

It is also absent in soles and in brills, species like this Bothus lunatus that live mainly resting on the seabed © Mickey Charteris

On one side, in a group of Osteichthyes the gaseous bladder assumes the functions of hydrostatic organ and becomes a valuable instrument, by means of which, by varying its gaseous contents, these fishes are able to adapt their own specific weight to that of the water where they do live and make vertical movements (swim bladder).

On the other side, in the most primitive forms of the Osteichthyes, Dipnoi and other groups, this organ works as a lung and in some species is assisted by accessory structures that allow them to breathe atmospheric air.

The swim bladder can be connected (physostome) or not (physoclist) to the pharynx, or may form relationships with the labyrinth by means of the Weber’s apparatus. To the swim bladder is associated with a thick net of capillaries, rete mirabile, that allows it to fill it with gas against gradient.

Among bony fishes are not rare hermaphroditic species changing sex with age. In the small clownfish communities, here Amphiprion ocellaris, for instance, reign the females, but when the queen dies the biggest male turns female and replaces her. It's matter then of protandrous hermaphroditism.

Among bony fishes are not rare hermaphroditic species changing sex with age. In the small clownfish communities, here Amphiprion ocellaris, for instance, reign the females, but when the queen dies the biggest male turns into female and replaces her. It’s matter then of protandrous hermaphroditism © Michael Eisenbart

The swim bladder has the walls covered by guanine, a nitrogenous substance that is also a component of the nucleic acids that render it waterproof and is equipped with a valve, called oval, utilized for deflating it. The shape of the bladder or, also, its absence, represent important elements in the systematics of these fishes.

The heart, where only venous blood passes, has two pumping cavities (one atrium and one ventricle) to which add a venous sinus and in some cases also an arterial cone.

Like the Cartilaginous fishes, also the Bony fishes are cold-blooded animals and the temperature of the body varies depending on the variations of the environment one (heterothermy). However the fishes of big dimensions and particularly active, are able to increase the temperature of their own body metabolically.

In the groupers, like in this Cephalopholis argus, when males are scarce it's the females who change sex and it's protogynous hermaphroditism.

In the groupers, like in this Cephalopholis argus, when males are scarce it’s the females who change sex and it’s protogynous hermaphroditism © Barry Fackler

Usually the sexes are separated, but there are known several cases of hermaphroditism. With few exceptions, the fecundation is external.

Most of the Bony fishes species are oviparous, but there is no lack of cases of ovoviviparity or of viviparity.

The eggs are usually very small and are spawned in a great number, at times several millions.

Upon birth the chicks may have an appearance quite similar to that of the adults or even very different. In this case they undergo a metamorphosis that in some cases can be very complex.

Distribution

The Osteichthyes are mostly oviparous, and sometimes we see mass matings like in this gathering of Lutjanus bohar with millions of eggs and clouds of sperm.

The Osteichthyes are mostly oviparous, and sometimes we see mass matings like in this gathering of Lutjanus bohar with millions of eggs and clouds of sperm © Richard Barnden

Widespread in all seas, from the surface up to depth of more than 9000 m, in brackish waters and in the fresh ones, the Osteichthyes represent the richest class of the Vertebrates and according to an estimate that should be considered very approximate they include a number of species presently extant from 20 thousand to 30 thousand.

The evolutionary history of the Osteichthyes is surely very complex and presents several situations of uncertainty , because of scientific contrapositions at systemic level.

Anyway it seems to be established on the base of fossil remains that already about 400 million years ago, between the end of the Silurian and the beginning of the Devonian, the ancestors of the Bony fishes have undertaken evolutionary paths that later on have developed along three different radiations: Palaeoniscidae, Dipnoi and Crossopterygii.

Conversely some carry them with themselves keeping them in mouth or stuck to the tail like this Phyllopteryx taeniolatus.

Conversely some carry them with themselves keeping them in mouth or stuck to the tail like this Phyllopteryx taeniolatus © Rafi Amar

It is to be kept in mind that, whilst the Palaeoniscidae became extinct at the beginning of the Jurassic, the histories of Dipnoi and Crossopterygii will have a destiny that will more or less directly interest the roots of the evolutionary radiation of the Vertebrates and that it will lead to the colonization of the subaerial environment.

Classification

The classification of the Osteichthyes is somewhat troubled and still subject of various hypotheses, each of which is supported by objective but partial data: as a consequence none of them appears completely satisfying. To complicate the landscape of the systematic of the Osteichthyes contribute the partial and therefore premature indications that originate from biomolecular investigations. In fact, the proposed classification, still in progress, presents different elements of contradiction with the traditional classification, based on morphological and  physiological characteristics.

The larvae are often quite different from parents, like this Leptocephalus of a moray eel who rolling up can form a gelatinous cylinder similar to a jellyfish.

The larvae are often quite different from parents, like this Leptocephalus of a moray eel who rolling up can form a gelatinous cylinder similar to a jellyfish © Mickey Charteris

About this, it is to be remembered that some Authors believe that the Brachiopterygii, considered by other specialists as a distinct subclass, are to be inserted in the Actinopterygii where they form an order of their own, that of the Polypteriformes.

In their turn, Dipnoi and Crossopterygii, after the opinion of other scholars form a monophyletic grouping, and so they should be united in a distinct class, that of the Sarcopterygii (or Coanoichthyes). Of opposite opinion are other scholars who believe that Dipnoi and Crossopterygii are a clearly polyphyletic grouping, therefore not natural, and they ascribe them to two distinct subclasses.

Here, more shareable appears to us the opinion of several scholars who consider the Osteichthyes a class of the Fishes and subdivide it in four groupings (taxa) to which is attributed the value of subclasses, Brachiopterygii, Actinopterygii, Dipnoi and Crossopterygii.

Finally, there are cases in the Osteichthyes of ovoviviparity or viviparity, and upon birth the newborns can have a look very similar to parents like for Hippocampus kuda.

Finally, there are cases in the Osteichthyes of ovoviviparity or viviparity, and upon birth the newborns can have a look very similar to parents like for Hippocampus kuda © Giuseppe Mazza

Consequently, regardless of the different points of view about the position and systematic subdivision of the Bony fishes, being the above mentioned groupings clearly different from each other, from the morphological and physiological point of view, here below we provide essential information concerning their distinctive characteristics. However, we must not forget that the class of the Osteichthyes remains such a vast as well as complex class and that, as a consequence, their systematics is susceptible to different opinions and modifications as research continues.

Subclass BRACHIOPTERYGII

Called also Arm-finned fishes or Cladistia, they form a very ancient group of Osteichthyes, appeared about 60 million years ago, at the end of the Mesozoic era during the Cretaceous, to which the status of subclass is attributed.

The traditional classification of Osteichthyes, is sometimes in contrast with biomolecular investigations, and is still subject of various hypotheses supported by objective but partial data. For instance this Polypterus is inserted by some specialists in the Chondrostrei, by other scholars in the Brachiopterygii and by some known taxonomists in the Dipnoi.

The traditional classification of Osteichthyes, is sometimes in contrast with biomolecular investigations, and is still subject of various hypotheses supported by objective but partial data. For instance this Polypterus is inserted by some specialists in the Chondrostrei, by other scholars in Brachiopterygii and by some known taxonomists in Dipnoi © Joel Abroad

Nowadays these fishes are represented by a few freshwater species of tropical and subtropical Africa known with the names of Bichir (Polypterus) and of Calabar squid (Erpetoichthys).

It should also be noted that the order to which it belongs, that of the Polypteriformes, here attributed to the subclass of the Brachiopterygii, by others instead is included among the Actinopterygii. Systematic placement apart, the name distinguishing the Brachiopterygii refers to the characteristic of its members of having the even fins short and equipped of their own musculature.

Moreover, the name of Polypteriformes originates from the particular morphology of the dorsal fin that is divided in several small pinnulae, each supported by a hard ray and by some soft ones. The body of these fishes is elongated, at times quite slender, rather anguilliform and may reach a total length of 1 m. The head, small and flattened, is covered by bony plates that form a sort of protective helmet.

And the same can be said for Erpetoichthys calabaricus. Here we consider the Osteichthyes a class with 4 subclasses: Brachiopterygii, Actinopterygii, Dipnoi and Crossopterygii.

And same can be said for Erpetoichthys calabaricus. Here we consider the Osteichthyes a class with 4 subclasses: Brachiopterygii, Actinopterygii, Dipnoi and Crossopterygii © Giuseppe Mazza

The skeleton of the head retains a very primitive structure, being partially cartilaginous with a limited number of ossifications. The remainder of the body of the Polypteriformes is covered by a robust armour formed by rhomboid scales of ganoidian type, articulated with each other and arranged to form oblique rows. The ventral fins, when present, occupy an abdominal position. The anal fin is little developed and the tail is diphycercal, symmetrical and ending in a point.

The Brachiopterygii are provided of a gaseous swim bladder, double and asymmetric, placed under the belly. The right lobe of the bladder extends to the anus whilst the left one reaches the stomach. In relation to its function as an accessory respiratory organ in support to the gills, the inner walls of the swim bladder are slightly pleated longitudinally and covered by ciliate scaly cells. The  Brachiopterygii  are equipped with functional spiracles and with spiral intestinal valve.  Presently these fishes are represented by  little more than a dozen of species, all belonging to the order of the  Polypteriformes. diffused in the internal waters of the African continent.

Polypterus endlicherii. The Brachiopterygii are just over ten species present in the inner waters of the African continent.

Polypterus endlicherii. The Brachiopterygii are just over ten species present in the inner waters of the African continent © Giuseppe Mazza

In its turn, the order is inclusive of the only family, that of the Polypteridae, divided in the genera Polypterus, with nine species known with the name of Bichirs, and Erpetoichthys (previously Calamoichthys), with 2 species, called Calamattidi.

These fishes live in the rivers and in the coastal lakes where they can be found in shallow waters and with sandy or muddy seabeds. Hidden on the bottom during the day, in the night hours they become particularly active. Besides swimming, they are able to proceed on the bottom thanks to their pectoral and ventral fins utilized as real legs.

Voracious predators, they feed on small fishes, worms, molluscs, amphibians and their larvae. With the arrival of the dry season, when there remain puddles with little muddy water, these fishes burrow into the ground and stand in a state of latent life until new rains do arrive. In this way, these animals are able to overcome such hostile and unusual conditions for a fish, thanks to the swim bladder that operates as a respiratory organ able to use the atmospheric oxygen.

Protopterus annectens has a primitive lung allowing him to breathe the air, buried in the muddy bed of the dry rivers, in a hibernation that may last even 4 years.

Protopterus annectens has a primitive lung allowing him to breathe the air, buried in the muddy bed of the dry rivers, in a hibernation that may last even 4 years © Gőtehal

During the reproduction season, it has been noted that the adults of these fishes leave the sites frequented during the dry season and move to the flooded areas where, after matings, the females lay very small and colourful eggs. From the fecundated eggs hatch larval-looking offspring that are characterized for having a golden body with longitudinal  black stripes, continuous dorsal fin and for being provided with external gills vaguely recalling those of the Dipnoi and of some Urodela Amphibians.

Among the most known species are to be mentioned the Bichir properly called (Polypterus bichir  Lacépède, 1803) diffused in the Nile waters and in those of the great African rivers and lakes, the Endlicher Bichir or Saddled Bichir (Polypterus endlicheri Heckel, 1847) and the Congo Bichir (Polypterus ornatipinnis Boulenger, 1902) that are met in the western part of Africa. In the slow and rich in vegetation waters of the low Niger and Cameroon is found the Calabar squid (Erpetoichthys calabaricus  Smith, 1865).

Subclass ACTINOPTERYGII

The Actinopterygii, here a Goldfish, developed in the Devonian freshwaters and invaded then also the seas giving life to almost all Osteichthyes.

The Actinopterygii, here a Goldfish, developed in the Devonian freshwaters and invaded then also the seas giving life to almost all Osteichthyes © G. Mazza

They are considered a grouping (subclass or class depending on the opinion) to which almost all  Osteichthyes. . are assigned. They are Bony fishes without choanae, that is without between the olfactory sacs and the oral cavity. Typically the pair fins are supported by rays arranged like a fan, hence also the common name of Ray-finned fishes.

It should be noted that the fins of the Actinopterygii do not present in their skeleton the basic structural organization for their evolution into the limbs of the terrestrial Tetrapods, as sometimes hypothesized.

Animals of very ancient origins, the Actinopterygii have left fossil remains witnessing their presence already during the Devonian period, between 400 and 350 million years ago. In the Carboniferous (360-285 million of years ago), between the Devonian and the Permian, the Actinopterygii, from the freshwater environments where they were quite common began to invade the seas, becoming the most numerous and most successful group of fishes.

Characterized by the rayed fins, the Actinopterygii accept any water and temperature, up to 2 °C, like this Pacific cod (Gadus ogac).

Characterized by the rayed fins, the Actinopterygii accept any water and temperature, up to 2 °C, like this Pacific cod (Gadus ogac) © Adam Maire

Presently, members of Actinopterygii are found in a great variety of environments, freshwater and also marine.

Also adapted to extreme environments, these fishes tolerate significant temperature variations, from just under 2° to almost 40 °C, of pH with levels varying from 4 to 10, and with quantity of dissolved oxygen between absence and saturation.

Some species live in sources of deserts (pupfishes), others in ephemeral pools, others more live in lakes and water streams at high altitude; species of Actinopterygii are found in underground grottoes (cavefishes). Some species live chiefly in the grottoes.

Some species populate the ocean waters, where they even reach depths of 7.000 m, like the deep water Anglerfishes (Oneirodidae of the order of the Lophiiformes).

And Chinook salmon (Oncorhynchus tshawytscha) leaps up the icy waters of Canada.

And Chinook salmon (Oncorhynchus tshawytscha) leaps up the icy waters of Canada © sfreeman7

Other species live in the cold waters of the polar seas, like the Greenland cod (Gadus ogac  Richardson, 1836) and the (Oncorhynchus tshawytscha Walbaum, 1792), sea and freshwater Salmonidae.

Presently the Actinopterygii gather about 25.000 species, practically the overwhelming majority of all Fishes and about half of all extant vertebrates. Also for this grouping, to which are ascribe the vast majority of the

Osteichthyes and of all Fishes, for the number of species they include as well as for the number of orders into which it is divided, are recorded significant divergences on their systematics.

We shall keep in mind the traditional classification that, on the basis of morphological, physiological and ecological  features, divides up the Actinopterygii in ChondrosteiHolostei and Teleostei, to which is recognized the value of infraclass.

Merlophius piscatorius can go down up to about 2000 m, but the deep waters anglerfishes reach the 7000.

Merlophius piscatorius can go down up to about 2000 m, but the deep waters anglerfishes reach the 7000 © Pietro Formis

It must be said, however, that it is not easy to identify the phyletic relationships existing between these three evolutionary lines of the Actinopterygii. These systematic uncertainties are also evidenced by the fact that various specialists instead insert Holostei and Teleostei in a distinct subclass, that of the Neopterygii. On the other hand, also the modern classification that utilizes molecular investigation instruments does not help much being still in the process of becoming and with several points of contradiction with the traditional one.

Infraclass Chondostrei

Classified in the past within the Cartilaginous fishes (Chondrichthyes), with whom they keep a certain morphological and structural similarity, they are considered an infraclass of Actinopterygii.

After traditional morphological classification, awaiting molecular studies, the Chondrostei gather about thirty species among which the sturgeons.

After traditional morphological classification, awaiting molecular studies, the Chondrostei gather about thirty species among which the sturgeons © Giuseppe Mazza

They gather together species with the skeleton having a certain degree of ossification, but that maintains completely cartilaginous parts, hence the name of Chondrostei.

In the past they were also classified among the Sharks (Chondrichthyes Selachimorpha) to which they look alike especially for the shape and the structure of the jaw that has no bone and for the presence of a couple of spiracles.

Except for Sturgeons, the Chondostrei are scaleless.

The Chondrostei unite about thirty species, commonly indicated with the names of Sturgeons (Acipenseridae) and Paddlefishes (Polyodontidae), ascribed to the order Acipenseriformes.

To these would be added the Mississippi paddlefishes, odd creatures like Polyodon spathula.

To these would be added the Mississippi paddlefishes, odd creatures like Polyodon spathula © Giuseppe Mazza

Some classifications include within the Chondrostei also the Bichirs (Polypterus) and the Calamattidae (Erpetoichthys) of the order Polypteriformes, included by us in the subclass of the Brachiopterygii.

In truth, the systematics of the Chondrostei, considered a paraphyletic grouping, that is, not including all the descendants of a common ancestor, is still under discussion.

Infraclass Holostei

The Holostei are considered an infraclass of Chondrostei. Mostly extinct, nowadays they are represented by species that are characterized for having a partially ossified skeleton and for the mouth armed with a string set of teeth.

The Holostei, here Amia calva, group together species mostly extinct with partially ossified skeleton and strong set of teeth.

The Holostei, here Amia calva, group together species mostly extinct with partially ossified skeleton and strong set of teeth © Phil’s 1stPix

They are provided with a pair of spiracles that however have been reduced to vestigial structures and that do not open to the outside.

Considered until a few years ago as a unitary clade, today instead, after cytogenetic investigations, several scholars consider the Holostei as a paraphyletic grouping.

Presently in the Holostei  are included two orders, Amiiformes and Lepisosteiformes,

The Amiiformes, appeared during the Middle Triassic (about 244 million of years ago), qualify to present the little ossified and for the most part cartilaginous skeleton. Presently they are represented only by the species Amia calva  Linnaeus (1766) living in the waters of the rivers of eastern North America.

Lepisosteus osseus, frequent in the eastern part of the USA, belongs to the same infraclass. In the profile recalls a pike but it is miuch more voracious.

Lepisosteus osseus, frequent in the eastern part of the USA, belongs to the same infraclass. In the profile recalls a pike but it is miuch more voracious © smmcdonald

The Lepisosteiformes, considered an order more archaic than the Amiiformes, are found in the fresh, brackish and, occasionally, also marine waters of North America, Central America and of the Caribbean islands.

The Lepisosteiformes include about ten species united in two genera, Atroctestus (Rafinesque, 1820), of Central America, and Lepisosteus (Linnaeus,1758), of the North America Great Lakes.

They are commonly known with the names of Caiman fishes, due to their long and thin snout, and also, improperly, of Pike fishes due to their resemblance to the true Pikes, fishes of the order of the Esociformes (Actinopterygii).

Infraclass Teleostei

They've come a long way the Teleostei! Born in early Triassic, they took advantage of the great mass extinction of Triassic-Jurassic to adapt with 20.000 species.

They’ve come a long way the Teleostei! Born in early Triassic, they took advantage of the great mass extinction of Triassic-Jurassic to adapt with 20.000 species © www.davidfleetham.com

Considered the modern Bony fishes, they form the most numerous grouping, not only within the Actinopterygii but also among all Fishes. The history of the Teleostei has begun during the Triassic (250-200 million years ago), period where their progenitors did appear.

But their evolutionary success is linked to the disappearance of almost all other Actinopterygii due to the huge great mass extinction that occurred in the Triassic-Jurassic (about 200-145 million years ago) when they were protagonists of a remarkable adaptive radiation. The success of the Teleostei did materialize with the differentiation of over 20 thousand species now known, distributed in more than 400 families in turn ascribed to  just more than 40 orders.

Given the notable biodiversity of the Teleostei, here we will limit ourselves to recall the most representative orders, referring to the taxonomic sheets for any further information.

Order Atheriniformes

Atherina boyeri is an about 10 cm Atheriniformes common in thick schools along the European Atlantic coasts, Mediterranean, Black Sea and Caspian Sea.

Atherina boyeri is an about 10 cm Atheriniformes common in thick schools along the European Atlantic coasts, Mediterranean, Black Sea and Caspian Sea © Giuseppe Mazza

They form an order where species of various appearances are distinguishable from each other mainly for skeletal characters. Usually these fishes have two dorsal fins where the fore one may be secondarily lost.

The lateral line has a vestigial form or is totally absent.

Practically spread in all seas, but the open, abyssal and polar waters, the order unites marine coastal, brackish, also freshwater species. Among the most known species of the order is to be mentioned the Big-scale sand smelt (Atherina boyeri  Risso 1810), an about 10 cm long small fish present in the Mediterranean waters.

A similar species, Atherina hepsetus, circulates only in the Mediterranean and in the Black Sea.

A similar species, Atherina hepsetus, circulates only in the Mediterranean and in the Black Sea © Frédéric Andre

Known also with the names of Big-headed smelt or Water-headed smelt, this species, present in some parts of the European Atlantic coasts, as well as in the Black and Caspian seas, where it seems that 2 subspecies have differentiated, respectively Atherina boyeri pontica (Eichwald, 1831) and Atherina boyeri caspia  (Eichwald, 1831). Another species of the genus is the Mediterranean sand smelt (Atherina hepsetus Linnaeus, 1758) small fish typical of the Mediterranean and the Black Sea.

Order Beloniformes

In the past inserted within the Cyprinodontiformes, now the Beloniformes are considered as an order of its own. Widely spread in salt and fresh waters, they include almost 300 species known for many commercial uses and for most of tropical Asia, distributed in the families AdrianichthyidaeBelonidaeExocoetidae, Hemiramphidae and Zenarchopteridae.

Belone belone with a prey. Known also as Garfish, it is an almost 1 m long Beloniformes, frequent in the Mediterranean waters, eastern Atlantic and Black Sea.

Belone belone with a prey. Known also as Garfish, it is an almost 1 m long Beloniformes, frequent in the Mediterranean waters, eastern Atlantic and Black Sea © Sarah Faulwette

Most of them are small, just under 10 cm, which makes them well suited for life in an aquarium.

In the Mediterranean are reported just 6 species of Beloniformes, very unique looking, like the Needlefishes (Belonidae) and Flying fishes (Exocoetidae).

The Needlefishes are so called due to the characteristic shape, very thin and elongated of their body. The jaws of these fishes, they also rather developed and thin, form a sort of a corneous beak armed with numerous teeth.

The Needlefishes belong to the Belonidae,  a family spread in the temperate and tropical seas that in the Mediterranean is present with the 4 species mentioned here below.

This Red Sea Tylosurus choram instead is in the "cleaning station" of a labrid who takes away from the relaxed predators the skin parasites and food stuck between the teeth.

This Red Sea Tylosurus choram instead is in the “cleaning station” of a labrid who takes away from the relaxed predators the skin parasites and food stuck between teeth © Rafi Amar

The Garfish (Belone belone Linnaeus, 1761), is a fish just under one metre long, per a weight that may even exceed the kg. The livery is simple, of silvery grey colour, darker on the back and whitish on the ventral parts. The skeleton presents a characteristic green-bluish colouration caused by the presence of bilirubin. It’s common in the waters of the Mediterranean, eastern Atlantic and of Black Sea.

The Short-beaked garfish (Belone svetovidovi Collette & Parin, 1970) has a range that includes the Mediterranean waters and some north-eastern sectors of the Atlantic. Easily mistaken with the common Garfish, this fish is mainly characterized by the number of the teeth.

The Keel-jawed needlefish (Tylosurus acus, Lacépède, 1803) is a mainly tropical species diffused in the Atlantic Ocean waters and in those of the Mediterranean where it is not very common.

To Beniformes, family of the Exocoetidae, belong also the flying fishes, able to twirl above the waves for 20-30 seconds.

To Beniformes, family of the Exocoetidae, belong also the flying fishes, able to twirl above the waves for 20-30 seconds © Harold Moses

Very similar in appearance to the common Garfish, this species is easily distinguishable due to its bigger size, up to 1,5 m, and by having more developed teeth and the caudal fin whose lower lobe is more extensive than the lower one.

The Red Sea houndfish (Tylosurus choram Rüppel, 1837) in its general appearance is quite similar to the common Garfish and in particular to the Keel-jawed needlefish. It lives in most temperate and warm seas and at times in the rivers. Very common in the westernmost part of the Indian Ocean, in the Red Sea and in the Gulf of Oman, is found also in the Mediterranean sea where it has entered through the Suez Canal (Lessepsian species).

To another species, that of the Exocoetidae, are ascribed the species of Beloniformes commonly as Flyingfishes or Flying cods.

The Mediterranean flyingfishes (Cheilopogon heterurus) glide by opening pectorals and ventrals, distinguish as have 4 wings.

The Mediterranean flyingfishes (Cheilopogon heterurus) glide by opening pectorals and ventrals, distinguish as have 4 wings © Harold Moses

The common name of these animals refers to the great development of the pectoral fins, that usually reach the dorsal fin and at times even the caudal.

This peculiarity is connected with the capacity of the Exocoetidae, unique for the fishes, to perform, precisely with the large pectoral fins used as wings, short flights over the surface of the water lasting 20-30 seconds.

The eyes are big and the mouth, small and turned upwards, has small teeth. Depending on the species, the ventral fins may be more or less developed, but always much less than the pectorals. On the base of the development of the ventral fins, are distinguished forms of four-winged Flyingfishes and of two-winged Flyingfishes.

Cheilopogon abei, present in the Indo-Pacific from African coasts to Solomon Islands, surprises for the lovely colour of the big pectoral fins.

Cheilopogon abei, present in the Indo-Pacific from African coasts to Solomon Islands, surprises for the lovely colour of the big pectoral fins © Максим Стефанови

The caudal fin is strongly forked, with the lower lobe longer than the upper one. The body of the Exocoetidae, usually from 20 to 40 cm long, is tapered and is covered by ample and hard scales. The livery of the adults is uniformly blue on the dorsal parts, silver white on the ventral. Otherwise, the juveniles can be variously coloured and have long barbels or pectoral fins with lively drawings.

These strange fishes are found in all the oceans, with greater frequency and abundance in warm waters. In the Mediterranean Sea are common the Sea swift and the Black wing flyingfish whilst more or less rarely can be met the flying fish and the Flying gurnard.

The Mediterranean flyingfish (Cheilopogon heterurus Rafinesque 1810) is mainly spread in the warm and temperate waters of eastern Atlantic Ocean and in western Mediterranean, where it is the most common species of the family.

Hirundichthys speculiger, frequent in tropics, has jumped out of water to escape Sula leucogaster that hunted by diving. But now the bird has emerged and preys from above.

Hirundichthys speculiger, frequent in tropics, has jumped out of water to escape Sula leucogaster that hunted by diving. But now bird has emerged and preys from above © Benoît Segerer

Usually about forty cm long, the Mediterranean flyingfish is a four-winged form having very long pectoral fins, besides the dorsal, and also the ventral ones that implant much far back. Another species of the genus is the Leaping flying fish or Abe’s flyingfish (Cheilopogon abei Parin, 1966), Exocoetidae spread in the waters of western Pacific and of the in the Indian Ocean.

The Black wing flyingfish (Hirundichthys rondeletii Valenciennes, 1847), usually about 20 cm long, is fairly common in the Italian seas. The species is characterized for being a four-winged form, having, besides the pectoral fins, also the ventral fins quite long and inserted much back. Spread in the Atlantic Ocean and in western Mediterranean, this species during the summer period goes up towards the upper Adriatic, whilst in winter it migrates towards the easternmost zones of the Mediterranean.

In the Gulf of Mexico, also this Hirundichthys volador of tropical Atlantic is hunted by the same surfacing species.

In the Gulf of Mexico, also this Hirundichthys volador of tropical Atlantic is hunted by the same surfacing species © Jon McIntyre

To this genus belong the Atlantic back wing flyingfish (Hirundichthys volador Giordania, 1884) that lives in north-western Atlantic Ocean, and the Mirrorwing flyingfish (Hirundichthys  speculiger Valenciennes, 1847) spread in circumtropical waters.

The Tropical two-wing flyingfish (Exocoetus volitans  Linnaeus, 1758) is a species quite common in the waters of the tropical belt. In the warm season it can enter the western Mediterranean and move, though rarely, up to the waters of the Adriatic Sea. Usually up to 20 cm long, the Tropical two-wing flyingfish is characterized for having the ventral fins very short and inserted forward (two wings shape).

The Blunt-snouted flyingfish (Exocoetus obtusirostris Günther, 1866) is very similar in the look and in the habits to the Tropical two-wing flyingfish from which it stands out at first sight due to the markedly shorter snout.

Exocoetus volitans is a species very common in the tropical belt waters and in summer it may enter the western Mediterranean.

Exocoetus volitans is a species very common in the tropical belt waters and in summer it may enter the western Mediterranean © Graham Ekins

Also this species is at times found in the Mediterranean waters. Among the many other species of the order of the Beloniformes we recall the following:

The Ricefishes and the Medakas, ascribed to the family Adrianichthyidae, in the past included in the order of the Cyuprinodontiformes, are met in the fresh and brackish waters in the area going from India to the Malayan archipelago, to Japan. The name of Ricefishes  with which some species are known comes from the fact that they are found also in the rice fields. These are rather small fishes, from 1,6 to -16 cm depending on the species. The small dimensions, associated to the facility of breeding and to the colouration of the livery renders these small fishes particularly appreciated by the aquarists.

The Japanese ricefish (Oryzias latipes Temminck & Schlegel, 1846), known also with the name of Medaka, is an euryhaline species and besides the rice fields, is found also in the slow waters of ponds, swamps and tidal pools.

Also the Japanese rice fish (Oryzias latipes) belongs to Beloniformes. About 3,6 cm long, it is a euryhaline species frequent in the rice fields, swamps and tide pools.

Also the Japanese rice fish (Oryzias latipes) belongs to Beloniformes. About 3,6 cm long, it is a euryhaline species frequent in the rice fields, swamps and tide pools © hhkaaks

Of small size, it usually measures about 3,6 cm of length, the Medaka has the body that in nature is of colour varying from cream white to yellowish. Popular for their variety of colours and forms and for their facility of breeding and of reproduction, since several centuries the Medakas are very appreciated as aquarium fishes. Considered very important also in the scientific field, the Medakas have been the first fishes whose genome has been completely sequenced, besides of having been genetically modified.

To another genus belongs the Duck-billed buntingi (Adrianichthys kruyti M.Weber, 1913), so called because of  its protruding upper jaw. It is a species of Ricefish typical of Lake Poso, in Central Sulawesi, Indonesia. It is a species under serious risk of extinction.

Order Bericiformes

The Beryciformes order groups marine fishes of night habits. They live mainly in deep waters. The showy Beryx decadactilus, for instance, goes down to around 1000 m..

The Beryciformes order groups marine fishes of night habits. They live mainly in deep waters. The showy Beryx decadactilus, for instance, goes down to around 1000 m. © Ken Sulak

They form an order whose species are present in the seas all over the world. Fishes with nocturnal habits, they live mostly in deep sea waters but some, like the species of Holocentridae, also frequent the shallow waters.

In the Mediterranean Sea waters have been reported 2 species, the Alfonsino and the Redcoat.

The Alfonsino (Beryx decadactylus Cuvier, 1829) is a fish the body of red colour, approximately rhomboid in shape, that can reach the length of 60 cm. The mouth is rather large and protractile, the eyes are remarkably large. The dorsal fin is higher in its fore portion. A similar shape has the anal fin that, however, is longer. The dorsal fin and the anal are supported by some weak spiniform rays. Of pelagic habits at depths exceeding the 1000 metre, the Alfonsino is spread in all seas, Mediterranean included, where however is fairly rare.

Sargocentron rubrum is frequent in tropical Indo-Pacific. From the Red Sea, like other Lessepsian species, has reached even the Mediterranen via Suez Canal.

Sargocentron rubrum is frequent in tropical Indo-Pacific. From the Red Sea, like other Lessepsian species, has reached even the Mediterranen via Suez Canal © Giuseppe Mazza

The Redcoat (Sargocentron rubrum Forsskål, 1775) populates the tropical waters of the Indian and Pacific oceans. It is present also in the Mediterranean with some limited populations in whose water has come after a Lessepsian migration, that is from the Red Sea through the Suez Canal.

Usually about 30 cm long, this fish has an oval body that is characterized for having pointed snout and a robust spine on each gill operculum. The eyes are big and the livery is showy, of bright red colour with longitudinal white stripes on the sides and with the fins edged with white. It lives in very varied environments, also in harbour waters, at low depth.

Order Cyprinodontiformes

The Cyprinodontiformes include mainly freshwater fishes with a frequent sexual dimorphism. They have small mouth, big eyes and only one dorsal fin, rounded, and symmetrical to the anal. Most species are small or medium sized: here a female of Heterandria formosa that measures just 8 mm.

The Cyprinodontiformes include mainly freshwater fishes with a frequent sexual dimorphism. They have small mouth, big eyes and only one dorsal fin, rounded, and symmetrical to the anal. Most species are small or medium sized: here a female of Heterandria formosa that measures just 8 mm of length © Giuseppe Mazza

They are an order of the Actinopterygii where are included mostly freshwater species which are mainly characterized by having small mouths, big eyes and fins supported by rays.  The dorsal fin is unique and the caudal is symmetrical and rounded. Most species are small and medium in size, between the 8 mm of the Least killifish (Heterandria formosa Girard, 1859) and the 34 cm of the Pacific four-eyed fish (Anableps dowei T.N.Gill 1861).

Usually the Cyprinodontiformes present a variously elongated body with a more or less developed lower jaw.

The sexual dimorphism is frequent  with the males having a more developed dorsal fin and a more showy livery than the females.

The American flagfish, Jordanella floridae reaches the length of 6-7 cm and is frequent in the fresh and brackish waters of Central America.

The American flagfish, Jordanella floridae reaches the length of 6-7 cm and is frequent in the fresh and brackish waters of Central America © Giuseppe Mazza

With over a thousand species, the order is amply spread in the seas and in the fresh waters practically of all the world.

Several species in the order, generally between 2,5 and 5 cm in size, are known with the name of killifish, i.e. stream fishes, and are found mainly in fresh or brackish waters of the American continent, from Canada up to Argentina. Some species of killifish live in Africa, in Asia and few species are known for Mediterranean Europe.

Due to the particular physiological and ecological characteristics, together with the beauty of the livery, several species of killifishes are subject of marketing and are bred all over the world. Among the killifishes is to remember the so-called Pupfishes, small fishes that are characterized by their capacity of survival in extreme and isolated conditions.

Similar dimensions, in Mediterranean, has Aphanius fasciatus, present also in brackish waters and only native Italian species of the genus.

Similar dimensions, in Mediterranean, has Aphanius fasciatus, present also in brackish waters and only native Italian species of the genus © Rolando Criniti

The pupfishes are small killifishes where most of the species present a marked sexual dimorphism in the shape of the body, and in the colouration of their liveries. Usually the livery of the males is markedly more showy than that of the females. Mainly diffused in environments of fresh and brackish waters of the American continent, the pupfishes feed on insects and weeds and of decaying plant material.

Some of them have a diet particularly rich in weeds like the well known Flagfish (Jordanella floridae Goode & Bean, 1879), a small fish, 6-7 cm long, amply spread in Central America where it is found in fresh and brackish waters.

Different is the diffusion of the Aphanius, genus of killifish diffused in the brackish and fresh waters of the coastal belt of Mediterranean where several species have differentiated, particularly threatened with extinction due to human anthropization.

To the genus Abableps are attributed several species, decidedly bigger, that usually measure 25-30 cm.

To the genus Abableps are attributed several species, decidedly bigger, that usually measure 25-30 cm © Pierre-Yves Le Bail

The Mediterranean banded killifish (Aphanius fasciatus Valenciennes, 1821), fish living in brackish waters, also in the salt marshes. With its circum-Mediterranean distribution, it is the only species of the genus considered as native to Italy.

Other species of the genus are the Guadalquivir toothcarp (Aphanius baeticus  Doadrio, Carmona & Fernandez-Delgado, 2002), reported for the coastal waters of south-western Spain, and the Spanish toothcarp (Aphanius iberus Valenciennes, 1846) is a species endemic to the coastal belt of the Mediterranean coast of the Iberian peninsula.

Finally, is to be reported the lake Tuz Anatolian giant killifish (Aphanius anatoliae Leidenfrost, 1912), that, with its length of 15 cm, is the giant of the genus. This species is reported for the basins of the lakes Tuz and Beysehir in Turkey.

They are frequent in the fresh and brackish waters of central and southern America. Here a small school of Anableps microlepis swimming.

They are frequent in the fresh and brackish waters of central and southern America. Here a small school of Anableps microlepis swimming © Mario Barroso

Still of the order of the Cyprinodontiformes we have to mention the Four-eyed fishes of the genus Anableps, so called due to the quite particular and very interesting conformation of its visual apparatus.

In fact, the eyes of these extraordinary fishes, big and protruding, are divided horizontally in two lobes by a membrane of epithelial tissue.

Also the retina, the cornea and the pupil are divided in two sections and equipped with two retinae. Conversely, the crystalline is unique.

In this way, while swimming with the eyes placed at the water surface, the Four-eyed fishes can have a vision of what happens over the surface and at the same time also under water. This capacity favours the predation on the insects they feed on.

Largescale four-eyes with its big scales (Anableps anableps) often present in the aquaria, is frequent from Venezuela to north Brazil.

Largescale four-eyes with its big scales (Anableps anableps) often present in the aquaria, is frequent from Venezuela to north Brazil © Giuseppe Mazza

To the genus Anableps are attributed various species that usually measure a length of 25-30 cm and which in nature live in brackish and fresh waters of the northern coast of Central and South America.

Besides the Largescale foureyes fish (Anableps anableps Linnaeus, 1758), the most known and sought after of the genus in fishkeeping, are to be mentioned also the common Foureyes (Anableps microlepis Müller and Troschell, 1844) and the Pacific four-eyed fish (Anableps dowii  T.N.Gill, 1861).

The African Rivulines are small killifishes of the Nothobranchiidae, family that, with more than 250 species, is native to the African continent south to Sahara.

Only 35 mm long, Nothobranchius guentheri is one of the order's jewels. It lives only in Zanzibar and unluckily, since 2018, appears as "Endangered" in the IUCN Red List.

Only 35 mm long, Nothobranchius guentheri is one of the order’s jewels. It lives only in Zanzibar and unluckily, since 2018, appears as “Endangered” in the IUCN Red List © Giuseppe Mazza

The Rivulines colonize environments of fresh and brackish water, and together with the Dipnoi, are the only fishes living in the extreme environments of the mud puddles of the African plains. Usually about 5 cm long, the African Rivulines have lively colours and some species, like Nothobranchius guentheri of Zanzibar, are rightly kept as aquarium animals.

Order Gasterosteiformes

They form an order of Actinopterygii Fishes amply diffused mainly in tropical and temperate environments of coastal marine waters, and, in a lesser extent, also of fresh waters.The order unites small species, having the body usually thin and elongated and with the caudal peduncle rather thinned out.

The Three-spined stickleback (Gasterosteus acukeauts) is present in the boreal hemisphere fresh, sea and brackish waters.

The Three-spined stickleback (Gasterosteus acukeauts) is present in the boreal hemisphere fresh, sea and brackish waters © Riccardo Novaga

The appearance of the Gasterosteiformes is rather various and in some cases the body is flat and wide with the mouth placed in ventral position and surmounted by a long rostrum and very ample pectoral fins (Pegasidae). Many species are equipped with lateral subcutaneous bony plates. The fins are supported by soft rays and by robust spiniform rays whose number forms a good taxonomic character. Few species do not have ventral fins, scales and also bony plates (Hypoptychidae).

In Europe the order is present only with a few species of Gasterosteidae known with the common name of Sandlances of which only one species (Gasterosteus aculeatus Linnaeus, 1758) reaches the western Mediterranean. Another species is the Sea stickleback (Spinachia spinachia Linnaeus, 1758), small fish about 20 cm long, diffused in the north-eastern Atlantic but absent in the Mediterranean waters.

Order Mugiliformes

The order of Mugiliformes has only one family, Mugilidae, with about 80 species. Mugil cephalus, common in Europe, goes up rivers and accepts any water, even polluted.

The order Mugiliformes has only one family, Mugilidae, with about 80 species. Mugil cephalus, common in Europe, goes up rivers and accepts any water, even polluted © Francesco Caroli

They are an order of fishes Actinopterygii to which are ascribed about 80 species commonly known with the name of Grey mullets and Mullets. The Mugiliformes include fishes with elongated body, of length from about 20 cm up to more than 120 cm, and with the mouth typically equipped with small teeth or totally toothless.

The pectoral and ventral fins are well developed. The dorsal fins are two, the first of which is sustained by 4 spiny rays whilst the second is formed by several thin and flexible rays. The caudal fin had two well developed lobes. The lateral line is barely noticeable.

The Mugiliformes include the only family of the Mugilidae to which are ascribed about 80 species of Grey mullets diffused mainly in the tropical and temperate coastal marine waters. Some species frequent the estuaries and also go up the fresh water courses.

Along the tropical coasts of western Africa and in America is very common also Mugil curema.

Along the tropical coasts of western Africa and in America is very common also Mugil curema © Allison & Carlos Estape

The Flathead grey mullet (Mugil cephalus Linnaeus, 1758), also known with the names of Volpina or Sea-mullet, is a fish having tapered body, covered by wide scales, of bluish grey colour on the back, whitish with dark streaks on the ventral parts.

Typically the head is broad and massive, with the mouth provided of small teeth and the eyes covered by a transparent eyelid. The two dorsal fins are separate and placed in the middle of the back and the ventral fins placed slightly behind the pectorals. The dimensions  usually can reach even 1 m of length and the weight may exceed 4 kg.

The Flathead grey mullet is a euryhaline species, that is able to stand ample variations of the degree of salinity, enough to live in marine, brackish and fresh waters. It also lives in polluted waters, and is frequently found inside the ports. The distribution area of the Flathead grey mullet is very vast and includes all the tropical and temperate belts of water. In the European seas it ventures to the north up to the Bay of Biscay.

Order Perciformes

The Perch (Perca fluviatilis) has given name to the order of the Perciformes, rich in more than 7000 species.

The Perch (Perca fluviatilis) has given name to the order of the Perciformes, rich in more than 7000 species © Giuseppe Mazza

Subject to conflicting opinions about their systematics, with more than 7000 species, the Perciformes form a grouping among the most numerous between all vertebrates.

The name of Perciformes comes from that of the European Perch (Perca fluviatilis Linnaeus, 1758), species certainly among the best known among all the representatives of the order. Known also with the simple name of Perch, this species has an average length of 20 cm but may even reach 60 cm. The dorsal parts of the body are of greenish colour adorned by 5-8 vertical bands, whilst the central ones are whitish.

Typically the fins have a very bright colour varying from the red to the orange, with the exception of the pectoral fins that are yellowish. It is a freshwater fish but decidedly euryhaline that especially in the northernmost areas is found in the open sea and also in the estuaries and in the brackish lagoons.

The ravenous Zander (Sander lucioperca), native to central-northern Europe and to western Asia,has been recklessly introduced in central-southern Europe.

The ravenous Zander (Sander lucioperca), native to central-northern Europe and to western Asia,has been recklessly introduced in central-southern Europe © Patrick Doll

Of distant Eurasian origins, the Perch is amply diffused practically in all Europe also as a result of human activities of introduction already since 1700.

The Pike-perch or Zander (Sander lucioperca Linnaeus, 1758) is a fish that in the oldest specimens can reach and even exceed the length of more than 1 m and the weight of 15 kg. The livery of the Pike-perch is of greenish brown colour on the head, dorsal parts and sides, lighter on the ventral parts. Some black vertical stripes run down from the back to the sides. The fins have a greenish colouration speckled with black.

Native to central-northern Europe and to western Asia, the Pike-perch is a voracious predator whose introduction in central-southern Europe happened in the early 1800s seems to have been the cause of serious problems of competition with the local fish fauna, including the disappearance of endemic forms.

Also the Ruffe (Gymnocephalus cernua), introduced for sport fishing in various European and American zones, is responsible of significant damage to local fish fauna.

Also the Ruffe (Gymnocephalus cernua), introduced for sport fishing in various European and American zones, is responsible of significant damage to local fish fauna © Ewout Knoester

The Ruffe (Gymnocephalus cernua Linnaeus, 1758) is a species that is met in environments of fresh waters of Europe and Asia, from France up to Siberia where it prefers sandy and gravelly bottoms.

It is a fish with a big head and body long up to 25 cm per a weight that may reach even 400 g, equipped with a big dorsal fin armed with erectile spines. The livery of the Ruffe has usually a brownish yellow colour with metallic reflections on the back, clear on the belly. It has mainly nocturnal habits. Often introduced for sport fishing in various European and American regions, also this species is responsible for significant damage to local fish fauna.

Another very known species of Perciformes is definitely the Fighting fish or Siamese fighting fish (Betta splendens  Regan, 1910). It is a small freshwater fish native to the hydrographic basin of the river Mekong in south-eastern Asia, where it’s found in stagnant, lake and river waters with weak currents.

Often present in the home aquaria, the males of the Betta (Betta splendens) are very territorial and do not tolerate the presence of other males.

Often present in the home aquaria, the males of the Betta (Betta splendens) are very territorial and do not tolerate the presence of other males © G. Mazza

It is rather frequent also in the rice fields and in poorly oxygenated waters. The species has been introduced during the last decades of the 1900s also in South America and in Indonesia.

Betta splendens has a robust and tapered body, with the males reaching the size of 6-8 cm and the females slightly stockier and smaller. The mouth opens in an upper position. Like all species of the family they belong to (Osphronemida), the Fighting fish has a labyrinthine type respiratory structure that allows it to breathe oxygen directly from the atmosphere. Due to this characteristic these fishes are known also as Labyrinthids.

The Fighting fish presents a sexual dimorphism that, besides in the size of the body and of the fins more developed in the males, manifests also in the livery.In the wild specimens, the livery of the males has a blue-greenish colouration with metallic reflections on the body, the head is black and the fins are red with blue-green metallic reflections.

Instead, the females are well accepted and reproduce also in modest-sized aquaria, creating for the eggs a characteristic floating nest of bubbles.

Instead, the females are well accepted and reproduce also in modest-sized aquaria, creating for the eggs a characteristic floating nest of bubbles © Giuseppe Mazza

Conversely, the female presents the body of brown colour with metallic reflections and adorned with two brown reddish longitudinal bands. However, the original phenotype is less available on the market, whilst are very widespread the colourful varieties obtained following a patient selection activity.

The male of the Fighting fish has a strong sense of territoriality and is of a particularly aggressive nature towards other males, to a greater extent during the breeding season. The worldwide fame of this species is linked to the aggressiveness of the males that has been exploited by the Thai, who run lucrative betting rings on the outcome of fights between two males, hence the common name of Fighting fish.

This practice is the basis of a traditional and careful selection activity with the purpose of obtaining stronger and more aggressive specimens and at the same time with a showy livery to exhibit on the occasion of the fighting and to introduce into the aquarium market.

To the same family of Betta, belongs also the Paradisefish (Macropodus opercularis) very much appreciated by the aquarists because of its splendid livery.

To the same family of Betta, belongs also the Paradisefish (Macropodus opercularis) very much appreciated by the aquarists because of its splendid livery © Peter Voigt

Another species fairly known as aquarium guest of the same family Osphronemidae, is the Paradisefish (Macropodus opercularis Linnaeus, 1758) diffused in freshwater environments of southeastern Asia and that also colonizes flooded forests and plains during the monsoon season.

The Paradisefish has a rather stocky and small body, usually is about 6-7 cm long, and typically presents the dorsal fin and the anal one long with a filamentous tip. The tail is elongated and biforked with the two lobes very ample. The pectoral fins are oval and the ventral ones are pointed.

The livery of the males is bright, more during the reproduction time. The head and the dorsal parts are green grey and the sides are bright red with electric blue lines. The ventral parts have a violet colouration. Also the fins have a colouration varying from violet to red, excepting the pectoral fins that are transparent. The tail is reddish adorned by a punctuation of blue. The females have a less lively colouration, usually light brown with reddish reflections.

The Boarfish (Capros aper), present in Mediterranean and in much of the Atlantic, has big eyes for hunting in the dark, between 100 and 500 m of depth.

The Boarfish (Capros aper), present in Mediterranean and in much of the Atlantic, has big eyes for hunting in the dark, between 100 and 500 m of depth © G. Mazza

The Boarfish (Capros aper Linnaeus, 1758) is a Perciformes that characterizes for the big eyes and the particularly elongated and pointed snout with protractile mouth. The dimensions are different in the two sexes with the males that usually do not exceed 15 cm and the females bigger, even 25 cm long.

There is only one dorsal fin with an evident incision; the ventral fins are rather big, the pectoral ones are small, and the ventral are quite developed. The tail is ample and flat. The body is red-orange, at times adorned by darker bends. During the breeding season, the livery is interested in an evident sexual dimorphism.

The Boarfish has a range that includes a good part of the Atlantic and the entire Mediterranean where it is found preferably on muddy bottoms, at depths usually varying between 100 and 500 m.

Order Pleuronectiformes

The Pleuronectiformes are characterized by flat fishes, like Pleuronectes platessa, with a blind and depigmented side as they spend almost all the day laid on the seabeds.

The Pleuronectiformes are characterized by flat fishes, like Pleuronectes platessa, with a blind and depigmented side as they spend almost all the day laid on the seabeds © Giuseppe Mazza

Called also Heterosomata, they form an order of Fishes Actinopterygii whose membres characterize for manifesting in the adult condition the body asymmetrical with both eyes located on the same side, defined ocular, whereby the opposite side is devoid of them (blind side).

In some species the ocular side is the right, in others it’s the contrary. Moreover, due to this particular physical conformation these fishes acquire a particular type of swimming called on one side, hence the scientific name of Pleuronectiformes.

The body of these fishes is very flattened laterally, slightly convex on the lateral side and flat on the blind side; this side is also depigmented, hence the common name of Flatfishes.

The eyes, normal when young, migrate growing on the pigmented side and so adults inclined.

The eyes, normal when young, migrate growing on the pigmented side and so adults inclined © Giuseppe Mazza

The body of the adults of Pleuronectiformes is covered with cycloid, ctenoid or tuberculate scales, with the two pectoral fins of different length, that of the ocular side more developed, the ventral ones reduced or missing and the uneven ones symmetrical.

Almost always the adults do not have the swim bladder.

The dimensions of the adults usually may vary from about 2 cm to more than 2,5 m in length of the Atlantic halibut or Halibut (Hippoglossus hippoglossus Linnaeus, 1758).

The livery is mimetic, usually of brownish colour marbled with dark and clear spots on the ocular side, uniform whitish in the blind.

In the larval stage, in fact, this Symphurus nigrescens had the eyes on the two sides like all fishes.

In the larval stage, in fact, this Symphurus nigrescens had the eyes on the two sides like all fishes © Stergios Vasilis

With more than 700 species, the Pleuronectiformes have a practically cosmopolitan distribution and most of them live on the muddy or sandy bottoms of the coastal waters where they spend most of their life leaning on the blind side, camouflaging with the surrounding environment.

Often they burrow onto the sand or into the mud of the bottom leaving their eyes free that protrude to see the approaching prey or to escape a possible predator.

Some species, like Hippoglossus hippoglossus are found up to 2.000 m of depth, others populate the deep water thermal springs, more still do live in freshwater environments.

Detail of a Bothus mancus, Pleuronectiformes of tropical Indo-Pacific. The eyes, raised from its body, move independently looking in every direction. They are those who drive the chromatophores changing drawings and colours, so much so that when missing or are covered by sand the fish can't interact and stays uniformly dark.

Detail of a Bothus mancus, Pleuronectiformes of tropical Indo-Pacific. The eyes, raised from its body, move independently looking in every direction. They are those who drive the chromatophores changing drawings and colours, so much so that when missing or are covered by sand the fish can’t interact and stays uniformly dark © Keoki Stender

Many species are of great economic importance and are subject to intensive fishing because they are a source of food for man.

Excellent swimmers, several species of the order, are used to do regular seasonal migrations moving from the most superficial waters of the feeding summer zones to the deeper ones of reproduction during the winter period. Here, the females lay pelagic eggs from where they will hatch larval forms presenting bilateral symmetry and swim like the other fishes.

The morphological difference of the larvae from the adults is such that for a long time they were considered as a taxonomic group itself. Later on the larvae lead a benthic life and undergo a transformation process with the migration of one eye to the opposite side of the head and the acquisition of a lateralized way of swimming.

The European flounder (Platichthys flesus) is a euryhaline species that can travel up rivers for long distances. Both eyes are on the right side of the body.

The European flounder (Platichthys flesus) is a euryhaline species that can travel up rivers for long distances. Both eyes are on the right side of the body © Hans Hillewaert

Among the many species of the order, we mention here the most well-known ones.

The European flounder (Platichthys flexsus Linnaeus, 1758) is a Pleuronectiformes measuring about 30-40 cm in length and with both eyes on the right side of the body. The species is characterized  for the presence of a series of spiny tubercles, formed by greater scales, placed at the base of the dorsal, anal and pectoral fins.

Euryhaline species, the European flounder is found on muddy and sandy bottoms and also in the lagoons and can go up the course of the river even for long distances. Its range is of disjoint type and includes the northern Atlantic up to Gibraltar Strait, North Adriatic and the Black Sea and the Azov one.

The Lemon sole (Microstomus kitt), native to the northern Europe seas, loves the shallow waters with pebbly seabeds, but can go down up to 200 m of depth.

The Lemon sole (Microstomus kitt), native to the northern Europe seas, loves the shallow waters with pebbly seabeds, but can go down up to 200 m of depth © Hans Hillewaert

The European plaice (Pleuronectes platessa Linnaeus, 1758) is a fish whose size may reach even 70 cm and with both eyes on the right side of the body. Typically, a bony crest is present behind the eyes. On the ocular side, the livery is brownish green enlivened by point-like spots of orange colour. The blind side is pearly white.

The European plaice is a marine species living on the muddy and sandy bottoms of the European shelf, usually at depths from 10 to 200 m, of the Barents Sea and of the eastern Atlantic Ocean, from Iceland to the Iberian Peninsula.

The Lemon sole (Microstomus kitt Walbaum, 1792) is native to the seas of northern Europe where it prefers the shallow waters with gravelling bottoms even at depths exceeding 200 m.

The Atlantic halibut or Halibut (Hippoglossus hippoglossus), the giant of the order with almost 3 m of length and about 230 kg weight, can even go down to 2000 m.

The Atlantic halibut or Halibut (Hippoglossus hippoglossus), the giant of the order with almost 3 m of length and about 230 kg weight, can even go down to 2000 m © Vsevolod Rudyi

The origin of the common name is uncertain and in any case it has nothing to do with the colour and neither with the taste of lemon. It is doubtful that the name limande may refer to the consistency of the skin, as hard as a “lime”, or to the fact that this fish is frequently found in the silt of the bottoms. The Lemon sole has a body reaching the dimensions of more than 60 cm, with the ocular surface, that is the right one, that gets a brown-reddish colouration, colourful with pink and orange and green and yellow spots. The side without eyes (blind) of the fish is whitish. Typically the mouth is very small and the caudal peduncle is ample.

Halibut is the English name with which are commonly indicated several species of Pleuronectiformes, but in particular it refers to the Halibut or Atlantic halibut (Hippoglossus hippoglossus Linnaeus, 1758), the giant of the order with more than 2,5 m of length per a weight of about 230 kg, to the Pacific halibut (Hippoglossus stenolepis Schmidt, 1904), and to the Greenland halibut or Black halibut (Reinhardtius hippoglossoides  Walbaum, 1792).

Also Hippoglossus stenolepis, present in the northern Pacific waters, is a big-sized Pleuronectiformes that may exceed the 2,5 m.

Also Hippoglossus stenolepis, present in the northern Pacific waters, is a big-sized Pleuronectiformes that may exceed the 2,5 m © Jackson W.F. Chu

Demersal fishes, the Halibuts live close to the bottoms and in the winter months, once the reproduction has occurred, they gather at the margins of the continental shelf on whose bottom they lay the eggs at depths between about 180 m and 500 m. Strong swimmers, the Halibuts are able to migrate on long distances and perform regular seasonal movements from the summer more superficial areas of feeding to the deeper reproduction ones during the winter period.

In particular the name of Halibut refers to the species of the genera Hippoglossus and Reinhardtius of which we mention the following.

Hippoglossus hippoglossus is a typical flat fish with a big mouth and with both eyes on the right side. The livery is of grey-brownish colour on the ocular side, whitish on the blind.

Much smaller, Limanda limanda, frequent in North European seas, rarely exceeds the 40 cm and 1 kg © Pat Webster @underwaterpat.

Much smaller, Limanda limanda, frequent in North European seas, rarely exceeds the 40 cm and 1 kg © Pat Webster @underwaterpat

Among the giants of the order, this fish reaches and exceeds even 2,5 m in length per a weight of about 230 kg.

Of benthic habits, the Atlantic halibut has a distribution extending in the northern Atlantic and in the Arctic Ocean where can be found on mobile seabeds as well as in open waters quite distant from the bottom.

The Pacific halibut (Hippoglossus stenolepis Schmidt, 1904) is a fish that may measure even 2,5 metres or more living in the waters of the northern Pacific. Usually the young specimens live in coastal waters and as they grow they move in deeper waters, at the margins of the continental shelf. It is predator of invertebrates, in particular crab, squids and clams, and also of other fishes.

Analogous is the size of the Common sole (Solea solea) present in the same waters but also in Mediterranean and Black Sea.

Analogous is the size of the Common sole (Solea solea) present in the same waters but also in Mediterranean and Black Sea © Frédéric ANDRE

The Greenland halibut or Black halibut (Reinhardtius hippoglossoides Walbaum, 1792), is quite similar in appearance to the Atlantic halibut from which it distinguishes for having the body more flattened and the mouth even bigger. The livery is of very dark brown colour on the ocular side as well as on the blind.

The Garve fluke or Common dab (Limanda limanda, Linnaeus 1758) is a small fish, usually from 20 to 40 cm in length per a weight that may reach even 1 kg, whose look is similar to that of the plaice, with both eyes normally on the right side of the body. Native to the shallow seas of North Europe, it is found in the coastal waters of north-eastern Atlantic, from the Gulf of Biscay to the North Sea to the western part of the Baltic Sea, where it lives preferably on sandy bottoms up to a depth of about 100 metres.

Lives on mobile sandy bottoms up to about 200 m of depth, but also in lagoons and in the estuaries brackish waters.

Lives on mobile sandy bottoms up to about 200 m of depth, but also in lagoons and in the estuaries brackish waters © Pierre Corbrion

The Common sole (Solea solea Linnaeus, 1758), is a Pleuronectiformes that on average measures about 30 cm but that may reach, though rarely, even the length of 50 cm. The snout is prominent and both eyes are placed on the right side (ocular). The only dorsal fin is longer than the anal, both are united by a membrane to the caudal fin that is small and rounded.

The livery is of colour varying from beige to greyish dotted with dark on the ocular side, whitish on the blind one. Amply diffused in the waters of the north-eastern Atlantic, of the North Sea and of the Baltic Sea, the common sole is frequent in the Mediterranean and in the Black Sea. It lives on mobile and sandy bottoms, only up to 200 m; it also frequents the brackish waters of estuaries and lagoons. Predator of night habits, spends the day hours sunken in the sand.

Very similar is Microstomus pacificus, present in the Pacific waters from the Bering Sea up to the coasts of Baja California.

Very similar is Microstomus pacificus, present in the Pacific waters from the Bering Sea up to the coasts of Baja California © Gregory C Jensen

The Pacific Dover sole (Microstomus pacificus Lockinghton, 1879), also called Slime sole or Slippery sole, is quite similar to the Common sole (Solea solea, Linnaeus, 1758). It is found in the waters going from the Bering Sea to those of Baja California.

The Naked sole (Gymnachirus nudus Kaup, 1858) is a small fish of about 12-15 cm, diffused in the waters of the western Atlantic, from the coasts of Mexico up to the Rio Grande do Sul in Brazil.

Known also with the name of Flabby sole, this species is found in coastal waters, from 2 up to about 130 m of depth on muddy and sandy bottoms.

Also the unusual looking fishes are not missing in the Pleuronectiformes, like the Naked sole (Gymnachirus nudus) present from Mexico to Brazil.

Also the unusual looking fishes are not missing in the Pleuronectiformes, like the Naked sole (Gymnachirus nudus) present from Mexico to Brazil © Mickey Charteris

The Elongate tongue sole (Symphurus ligulatus Cocco, 1844) has an elongated body, usually about 10 cm long, with the dorsal fin supported by more than 100 rays. The livery has a yellowish brown colouration with brownish spots on the ocular side, whitish on the blind one.

It is spread in the tropical and subtropical band of the eastern Atlantic and frequently also in western Mediterranean, where it is not rare. It carries on a benthic life on sandy or muddy bottoms between 200 and 800 metres of depth.

The fish Dog’s tongue (Symphurus nigrescens Rafinesque, 1810) looks a lot like the Elongate tonguesole from which however diggers as having a stockier body, usually just over 10 cm long, and for the least number of rays of the dorsal fin, less than 90.

The profile of the Blackcheek tonguefish (Symphurus plagiusa) abundant in the West Atlantic and in brackish waters

The profile of the Blackcheek tonguefish (Symphurus plagiusa) abundant in the West Atlantic and in brackish waters © johnwilliams

The livery is brownish marbled with clear and dark spots irregularly arranged. The dorsal and the anal fins are merged with the caudal one like in the eels. The pectoral fins are missing. The fish Dog’s tongue is found in the warm waters of the tropical band of eastern Atlantic and also in the Mediterranean where however it is fairly rare.

The Blackcheek tonguefish (Symphurus plagiusa Linnaeus, 1766) is a Pleuronectiformes of about 20 cm or little more that differs for the presence of a big blackish spot on the operculum. Demersal species, it’s diffused in western Atlantic where it is very abundant on the soft bottoms of the coastal and brackish waters, up to about 180 m of depth.

Order Scorpaeniformes

The Scorpaeniformes group together more than 300 species mostly marine or brackish, but are found also like this Cottus gobio in cold fresh waters with strong currents.

The Scorpaeniformes group together more than 300 species mostly marine or brackish, but are found also like this Cottus gobio in cold fresh waters with strong currents © Julien Renoult

They represent an order to which are attributed more than 300 species, mostly amply diffused in all seas, polar ones included. Several species populate the brackish and fresh waters and some are found in cold fresh waters and with strong currents, like the European bullhead (Cottus gobio Linnaeus, 1758), and the Sculpin (Cottus scaturigo, Jörg Freyhof et alii, 2005) of uncertain taxonomic value.

The dimensions of the Scorpaeniformes  vary from the about 4 cm in length of the Paraliparide (Eutelichthys leptochirus Tortonese, 1959), species exclusive to the Mediterranean where is very rare, to to almost 80 cm of the

Cabezon (Scorpaenichthys marmoratus Ayres, 1854), diffused in the north-eastern Pacific Ocean waters, from Alaska to California.

Said for its voracity Red lionfish, but also Scorpionfish for the poisonousness of the dorsal rays and Ornate butterfly-cod for its feathers elegance, Pterois volitans is native to tropical waters of the east Indian and Pacific oceans, but was accidentally introduced in Florida causing major damage to the local and Caribbean species.

Said for its voracity Red lionfish, but also Scorpionfish for the poisonousness of the dorsal rays and Ornate butterfly-cod for its feathers elegance, Pterois volitans is native to tropical waters of the east Indian and Pacific oceans, but was accidentally introduced in Florida causing major damage to the local and Caribbean species © G. Mazza

Many species are armed with poisonous spines on the body and on the fins. Of predatory habits, they live in various environments.

Several species are diffused in the marine and brackish waters of the oceans of the boreal hemisphere, especially in the boear and even arctic ones, some species are abyssal, like the Abyssocottidae, endemic to the deep waters of Baikal Lake, in Siberia.

In the Mediterranean Sea are present the extremely rare Longspined bullhead (Taurulus bubalis Euphrasen, 1786), small fish whose dimensions usually stand on 12 cm in length, and the already mentioned Paraliparide (Eutelichthys leptochirus  Tortonese, 1959), small fish endemic to the deep waters of the Mediterranean Sea.

We find the typical features of the order also in this Shortspine scorpionfish (Dendrochirus brachypterus), a Scorpaeniformes with the scientific name of the genus coming from the Greek Dendron (tree) and Cheiros (hand) referring to the open pectorals drawing the characteristic concentric growth circles of a cut tree trunk.

We find the typical features of the order also in this Shortspine scorpionfish (Dendrochirus brachypterus), a Scorpaeniformes with the scientific name of the genus coming from the Greek Dendron (tree) and Cheiros (hand) referring to the open pectorals drawing the characteristic concentric growth circles of a cut tree trunk © Giuseppe Mazza

Among the most typical representatives of the order are the species known as Scorpionfishes and Lionfishes.

The Red lionfish (Pterois volitans Linnaeus, 1758), known also as Turkeyfish and Ornate butterfly-cod, is a fish usually measuring little less than 40 cm in overall length.

It is characterized by the small head with wide mouth and big and protruding eyes; on the chin and over the eyes stand two small growths. The body, dorsally curved and  ventrally flat, narrows into a long, wide and roundish tail.

The first rays of the dorsal fin and of the anal are poisonous spines that are erected in case of danger.

There is also a yellow and black version, a real jewel not exceeding the 15 cm, with aquarists ready to pay any price to have it.

There is also a yellow and black version, a real jewel not exceeding the 15 cm, with aquarists ready to pay any price to have it © Ian Shaw, Reef Life Survey

Spread in the Pacific Ocean and Red Sea waters, the Red lionfish lives on stony seabeds usually up to 150 m of depth. During the last century the species has been accidentally introduced in the Atlantic Ocean and recently has been repeatedly reported also in Mediterranean waters.

The Dwarf lionfish (Dendrochirus brachypterus Cuvier, 1829) is a marine Scorpaeniformes whose size rarely is just over 15 cm long.

Known with various names, among which Shortspine scorpionfish or Short-finned turkeyfish, this fish is characterized by the presence of a sort of a small tentacle over each eye and by leaf-like appendages of various development on the head and along the lateral line. The dorsal fin is equipped with poisonous spines, hence the common name of scorpion.

Similar dimensions has Scorpaena maderensis of eastern Atlantic, common in Madeira but also in the Mediterranean.

Similar dimensions has Scorpaena maderensis of eastern Atlantic, common in Madeira but also in the Mediterranean © Giuseppe Mazza

Of nocturnal habits the Dwarf lionfish is a predator of small crustaceans diffused in the Pacific and Indian oceans waters.

The Madeira rockfish (Scorpaena maderensis Valenciennes, 1833), is a marine Scorpaeniformes of small dimensions that usually do not exceed 15 cm. The livery is of varying colour, from black to red but usually of light brown colour marbled with darker spots.

Diffused in the eastern Atlantic, where it is common in Madeira, hence the specific name, this species is also found in the Mediterranean. Known also with the name of Scaly scorpionfish, this fish lives in the coastal waters among the thick vegetation of hard seabeds.

The Red scorpionfish (Scorpaena scrofa), with analogous range, is instead the giant of the genus with a record of 3 kg and 50 cm.

The Red scorpionfish (Scorpaena scrofa), with analogous range, is instead the giant of the genus with a record of 3 kg and 50 cm © Giuseppe Mazza

The Red scorpionfish (Scorpaena scrofa Linnaeus, 1758) stands among the largest ones between the congeneric species reaching even 50 cm in length. It has a stocky head equipped with spines and with flesh appendages.

Usually the livery is of bright dark variegated red colour and has a black dot on the dorsal fin; less frequently are met specimens of yellow, pink or brown colour. The Red scorpionfish is found in the eastern Atlantic and in the Mediterranean where it lives on hard or coralligenous seabeds, from a few to about 200 of depth.

The Black scorpionfish (Scorpaena porcus Linnaeus, 1758) called also European scorpionfish, is a fish Scorpaeniformes who like the other species of the genus characterizes for having stocky head adorned with typical fleshy appendages and spines.

Rare image of a Stonefish (Synanceia verrucosa) swimming. Similar to a rock, it's the most fearful and poisonous membre of the order.

Rare image of a Stonefish (Synanceia verrucosa) swimming. Similar to a rock, it’s the most fearful and poisonous membre of the order © Frank Käck

Diffused in a vast range that includes eastern Atlantic, Mediterranean and Black Sea, the Black scorpionfish is found mainly on rocky seabeds or among posidonia meadows. As in the other components of the order, the spines of the fins of this fish are connected to poison glands.

The most dangerous of the Scorpaeniformes is however the Stonefish (Synanceia verrucosa) present in low waters of tropical Indo-Pacific. Camouflaged on the seabed, it has on the back 12-14 solid grooved spines, each connected at the base to two glands full of poison. They are able to pierce the sole of a light shoe and inject the most powerful poison in the world of the fishes, deadly even for man. Its composition is very similar to that of the cobra, and in case of sting it is necessary to intervene immediately with the specific serum.

Order Stephanoberyciformes

Stephanoberyx monae. The Stephanoberyciformes are rare and little known fishes living upto almost 5.000 m of depth in all seas, but the Mediterranean.

Stephanoberyx monae. The Stephanoberyciformes are rare and little known fishes living upto almost 5.000 m of depth in all seas, but the Mediterranean – NOAA Okeanos Explorer Program

They are considered an order of Fishes Actinopterygii where are grouped about sixty species that differ for having the head, usually big , covered by bony crests and spines.

The Stephanoberyciformes. are rare fishes and little known living in the depths of the seas of the whole world, except the Mediterranean Sea.

The type species is the Pricklefish (Stephanoberyx monae Gill, 1883), small fish living in the waters of the Atlantic at depths included from about 900 m up to about 5.000 m).

Order Synbranchiformes

The Spiny eel (Mastacembelus platysoma) lives in the Tanganyika Lake in Africa. Has elongated body with a series of dorsal spines and tubular nostrils.

The Spiny eel (Mastacembelus platysoma) lives in the Tanganyika Lake in Africa. Has elongated body with a series of dorsal spines and tubular nostrils © Ad Konings

They are an order still quite controversial to which are ascribed numerous freshwater and brackish water species whose scientific name refers to the fact that the gill openings converge in a single ventral opening. Because of their similarity in appearance with the Anguilliformes, from which however they are distinguished for having the fins supported by spiny rays, the Synbranchiformes are often called swamp eels.

They are fishes with naked bodies, up to 150 cm long. They have continuous dorsal fins and lack of pectoral fins and, at times, of the pelvic ones. The Synbranchiformes lack the swim bladder and are able to live out of water for long periods of time.

With about one hundred species, the Synbranchiformes are spread in almost all marshy environments of freshwater and brackish waters of south-eastern Asia, of India and of Australia and also of tropical America and Africa.

The Blind swamp eel (Ophisternon infernale) is a Synbrachiformes present only in the caves of Mexico.

The Blind swamp eel (Ophisternon infernale) is a Synbrachiformes present only in the caves of Mexico © indie peach nature

Reported in an ample range that includes rivers and marshes of freshwater and brackish water of southern Asia and of Oceania, the Bengal eel (Ophisternon bengalense McClelland, 1844) is a species with little-known biology.

Another species of the order with triglobont habits is the Blind swamp eel (Ophisternon infernale Hubbs, 1938).  This is a fish with a globose head rich in sensory pores and with an elongated and vermiform body that measures on average 30 cm.  As the common name indicates, in relation to life in a hypogean environment devoid of light, the Blind swamp eel. has no eyes and has the body having no scales and pigment.

Known for the Yucatan in Mexico, the Bland swamp eel is found in shallow freshwater, under the stones or among the mud of dolines and calcareous caves. It feeds on small crustaceans and on the droppings of bats and swallows.

Even 150 cm long, the Marbled swamp eel (Synbranchus marmoratus) moves also out of water, among ponds, canals and rice fields in central and southern America. Thanks to the presence of a rich net of blood vessels on the mouth covering, this unusual Synbrachiformes is able to breathe also the oxygen present in the air.

Even 150 cm long, the Marbled swamp eel (Synbranchus marmoratus) moves also out of water, among ponds, canals and rice fields in central and southern America. Thanks to the presence of a rich net of blood vessels on the mouth covering, this unusual Synbrachiformes is able to breathe also the oxygen present in the air © Lucas Fornero

Always in the Synbranchiformes, is to be mentioned Mastacembelus platysoma (Poll et Matthes, 1962), known as Spiny eel and present in the lake Tanganyika, in Africa. Similarly to the congeneric species, as its vulgar name states, this species has the appearance of an eel, with elongated body and a series of dorsal spines. The snout is well developed and equipped with a pair of tubulated nostrils. Its dimensions reach an average length of little more than 15 cm.

The Marbled swamp eel (Synbranchus marmoratus Bloch, 1795), is a fish that may measure even 150 cm in length that distinguishes for the presence of vestiges of the dorsal and anal fins and the absence of the pectoral and pelvic ones. Thanks to the presence of a rich network of blood vessels on the casing of the mouth, the Marbled swamp eel, diffused in central and southern America where it is found in waters of ponds, canals and rice fields, is also able to breathe atmospheric oxygen.

Order Syngnathiformes

Syngnathiformes have small mouths on a tubular snout. They often live among the weeds and the Leafy seadragon (Phycodurus eques) perfectly imitates their details.

The Syngnathiformes have small mouths on a tubular snout. They often live among the weeds and the Leafy seadragon (Phycodurus eques) perfectly imitates their details © Rafi Amar

They are considered an order of Actinopterygii, whose composition and systematic position are still now rather controversial, to which are ascribed species having a quite unique look like Trumpetfishes, Needlefishes, Seadragons, Seahorses and more.

Apart from the look, these fishes are characterized by having small mouths opening on a tubular snout, hence the scientific name, literally “joined jaws”, whose length varies depending on the habits of the prey they eat. The snout is shorter in the species feeding on the invertebrates living on the seabed, more developed in those feeding on preys, usually tiny shrimps, that they suck while swimming in the water column.

The body of the Syngnathiformes  is rigid and semi-flexible, with a narrow and elongated shape, covered by bony plates and typically surrounded by a series of bony rings.

Phyllopteryx taeniolatus is another seadragon, but besides these the Syngnathiformes include the well known seahorses, pipefishes, trumpetfishes and others more.

Phyllopteryx taeniolatus is another seadragon, but besides these Syngnathiformes include the well known seahorses, pipefishes, trumpetfishes and others more © Rafi Amar

The fins are small and allow very slow movements, giving these fishes little opportunity to escape predators or to successfully pursue a possible prey.

Several representatives of the order have the habit of living among the weeds, where they camouflage for the look and for the fact of swimming, keeping the body aligned vertically, with the head up and the tail down. The tail itself is used as a prehensile organ with which the animal attaches itself to the algae or to the gorgonians.

Furthermore, as important strategy of defense and of food, some Syngnathiformes have the capacity to modify the colour of their own body in a short time or to make grow further leafy dermal growths that are not used for moving ut serve only as camouflage with the seaweed where they do live.

Hippocampus hippocampus, frequent in Mediterranean and east Atlantic, is among the most known. Has sharp head, short snout and no outgrowths.

Hippocampus hippocampus, frequent in Mediterranean and east Atlantic, is among the most known. Has sharp head, short snout and no outgrowths © Glenn Biscop

This ability appears enhanced in the Leafy seadragon (Phycodurus eques (Günther, 1865), fish native to the marine waters of southern and western Australia and of Tasmania.

Another particularly distinctive feature of the species of the order is their reverse sexual organization, called “male pregnancy” where the females lay the eggs inside an incubator bag the males carry on the belly, close to the anal opening.

In this way the males carry with them the eggs that meanwhile develop in the embryos that are nourished by the capillaries that surround the eggs. When the eggs hatch, the males expel through abdominal contractions the newborn babies who are very similar to the adults.

Conversely, these abound in the Long-snouted seahorse (Hippocampus guttulatus), with similar range but present also in the Black Sea.

Conversely, these abound in the Long-snouted seahorse (Hippocampus guttulatus), with similar range but present also in the Black Sea © Maurizio-Pasi

Several species of this order are seriously threatened by inappropriate human activities that have caused the serious degradation of their habitat and by the increased foreign demand for their utilization as tourist souvenirs and also in Chinese traditional medicine.

Also the trade of live specimens in the breeding of fishes in domestic aquaria stands among the causes of the worrying decline in the populations of seahorses in many Asian countries.

These particular fishes are practically diffused in all tropical subtropical and warm temperate seas and are found mainly in habitats with seaweeds, in the coral reefs and among the mangroves. Several species go up the rivers and settle in freshwater habitats.

The White's seahorse or Sydney seahorse (Hippocampus whitei) lives along the south-western coasts of the Pacific Ocean.

The White’s seahorse or Sydney seahorse (Hippocampus whitei) lives along the south-western coasts of the Pacific Ocean © David Harasti

Among the many species included in the Syngnathiformes we mention the following.

The Mediterranean Short-snouted seahorse (Hippocampus hippocampus, Linnaeus, 1758), is one of the most known species. It has the body, usually just under 30 cm long, devoid of dermal excrescences, more or less multicoloured, varying from yellow to greyish pink or brown. The head is pointed, with a rather short snout. The pectoral fins are little developed. It is found in the waters of the Mediterranean Sea and of eastern Atlantic Ocean, usually among the algae to which it attaches itself with the tail and with which it camouflages perfectly.

The Long-snouted seahorse (Hippocampus guttulatus Cubier, 1829,) is a species similar to the Mediterranean sea horse from which differs mainly for the presence of pointed dermal outgrowths along the body and the head.

Frequent in the domestic aquaria, the Yellow seahorse or Spotted seahorse (Hippocampus kuda) has rounded protuberances.

Frequent in the domestic aquaria, the Yellow seahorse or Spotted seahorse (Hippocampus kuda) has rounded protuberances © Giuseppe Mazza

It reaches the maximum size of 15 cm and has a very varied colouration, at times brightened by white longitudinal  stripes. The Long-snouted seahorse lives in the waters of the Mediterranean, of eastern Atlantic and of Black Sea, usually at depths less than thirty metres.

The White’s seahorse (Hippocampus whitei Bleeker, 1855), known also with the names of New Holland seahorse and of Sydney seahorse, mentioned only for the south-western coastal waters of Pacific Ocean. On average about 10 cm long, this fish has a body equipped with spines with a narrow head and well developed snout. Usually the livery is of colour varying from pale brown to dark brown or black, sometimes wholly yellow.

The Coleman’s pygmy seahorse (Hippocampus colemani Kuiter, 2003), reported in the coastal waters off Lord Howe Island in Australia, is a species with a chorology still poorly defined.

Discovered only by chance in 1969, the Pygmy seahorse (Hippocampus bargibanti) measures less than 2 cm and spends whole life on a gorgonian.

Discovered only by chance in 1969, the Pygmy seahorse (Hippocampus bargibanti) measures less than 2 cm and spends whole life on a gorgonian © Francois-Libert

It is a small seahorse, about 2,5 cm, with a small head and short snout. The colour is usually variable from whitish to yellowish, adorned with narrow circular or elliptical bands from whitish to thin red lines on the trunk, dark brown bands that radiate from the eye and red-brownish appendages. The tail is brown with red marks.

The Yellow seahorse or Spotted seahorse (Hippocampus kuda Bleeker, 1852), is a Syngnathiformes whose dimensions maintain between 20 and about 30 cm.

The body, equipped with rounded and devoid of spine protuberances, has a relatively big head with short and stocky snout. The tail is prehensile. The livery is of various colours, going from beige to yellow with numerous dark dots.

The Longsnout seahorse (Hippocampus reidi) is the most skilled in the mimetic camouflage with incredible changes of colour in predefined zones.

The Longsnout seahorse (Hippocampus reidi) is the most skilled in the mimetic camouflage with incredible changes of colour in predefined zones © Terence Zahner

The Yellow seahorse is found in south-eastern Pacific where it frequents the phanerogam meadows in coastal waters, estuaries and even harbours of Asian south-east.

The Bargibanti Pygmy seahorse or Bargibant’s seahorse (Hippocampus bargibanti (Whitley, 1970), is a tiny fish whose size usually does not exceed 2 cm. Of typical appearance of the Syngnathidae, the Pygmy seahorse has a vertical body, elongated equine-shaped head and prominent and rounded ventral parts.

Diffused in the Indian and Pacific oceans waters, this species lives exclusively on gorgonians of the coral reefs with which it merges with a livery that imitates them in the livery and in the shape.

Poorly visible, due to outgrowths and the size not exceeding 5,5 cm, is also the odd Idiotropiscis australis, one of the pygmy pipefishes endemic to Australian seas.

Poorly visible, due to outgrowths and the size not exceeding 5,5 cm, is also the quite odd Idiotropiscis australis, one of the pygmy pipefishes endemic to the Australian seas © J. Martin Crossley

The Longsnout seahorse (Hippocampus reidi Ginsburg, 1933), known also with the name of Slender seahorse, reaches an average length just over 15 cm.

Usually the livery is different in the two sexes with the females of yellow colour and the males orange, at times enlivened by sporadic brown or pale spots. The species is amply diffused in the western Atlantic waters where often lives attached to the gorgonians or to the marine phanerogams.

Pygmy pipehorses is the name with which are commonly indicated the species of Idiotropiscis (Whitley, 1947) due to their small size. Presently in genus are ascribed 3 species of Pygmy pipehorses endemic to the Australian seas of which the best known is the tiny Southern little pipehorse, Idiotropiscis australis (Waite and Hale, 1921).

Macroramphosus scolopax, called Longspine snipefish due to the long tubular "snout", as Syngnathiformes, can go down to 500 m of depth.

Macroramphosus scolopax, called Longspine snipefish due to the long tubular “snout”, as Syngnathiformes, can go down to 500 m of depth © Giuseppe Mazza

With the name of Seamoth are commonly indicated some species of Syngnathiformes that are characterized for having the body flattened with well developed snout and the presence of large wing-like pectoral fins. Moreover, the Seamoths have the pelvic fins modified with which they “walk” on the bottom of the sea where they live.

The Seamoths form the family of the Pegasidae to which are presently ascribed 5 species, whose dimensions usually are included between 10 and 20 cm, native to the Pacific and Indian oceans where they are found among the coral reefs. The most known species is the Short dragonfish or Little dragonfish (Eurypegasus draconis  Linnaeus, 1766).

The Longspine snipefish (Macroramphosus scolopax Linnaeus, 1758), is a species with the body laterally compressed and without scales, whose dimensions usually keep under 20 cm.

Even 1 m long, with changing mimetic livery, the Caribbean Trumpetfish (Aulostomus maculatus) hunts in ambush hidden by the corals or by moving predators.

Even 1 m long, with changing mimetic livery, the Caribbean Trumpetfish (Aulostomus maculatus) hunts in ambush hidden by the corals or by moving predators © Kevin Bryant

Equipped with a long tubular “snout” at the apex of which opens the small mouth, hence the common name with which is indicated, the Trumpretfish has typically the first dorsal fin provided of a robust and long toothed spine; the second dorsal is very small.

The livery is uniformly silvery in colour with pink hues. The presence of this fish has been reported for the temperate and subtropical waters of the eastern Atlantic, the Mediterranean, from 50 to 500 m of depth.

With the name of West Atlantic Trumpetfish, Aulostomus maculatus (Valenciennes, 1841), is a Syngnathiformes that may reach even the length of 1 m.

Analogous is the chromatic variability, the size and the opportunistic behaviour of the Chinese trumpetfish (Aulostomus chinensis) hiding also behind the turtles.

Analogous is the chromatic variability, the size and the opportunistic behaviour of the Chinese trumpetfish (Aulostomus chinensis) hiding also behind the turtles © G. Mazza

It is a fish with elongated body with a big head anf the mouth turned upwards that in the appearance recalls a small trumpet, hence the common name, and with several filaments having a tactile function that are implanted on the lower lip.

The fins are located on the lower part of the body and often are kept folded. Endowed with strong camouflage capabilities, the West Atlantic trumpetfish is able to modify the colour of its own body depending on the environment and, like in the males, while courting. The species is reported for the waters of the Atlantic where prefers the environments of algae and of coral reefs.

The Chinese trumpetfish (Aulostomus chinensis Linnaeus, 1766), has the body compressed laterally reaching the average size of about 80 cm. The species is distinguished by the long tubular snout with protrusible mouth and equipped with a small barbel on the lower apex.

The Sargassum pipefish (Syngnathus pelagicus) is present in west Atlantic, from Nova Scotia to Brazil.

The Sargassum pipefish (Syngnathus pelagicus) is present in west Atlantic, from Nova Scotia to Brazil © Pauline Walsh Jacobson

The dorsal fin is subdivided in two parts of which the first is formed by isolated spines whilst the second is a smal fin similar to the underlying anal fin.

Also the pelvic fins are little developed and are adorned at the base by a black spot. The livery is varied, uniform or variegated in several shade of colour, from grey to brown, to dark green. Some phenotypic varieties appear uniformly of bright yellow colour. Usually the rear part of th body is blackish and dotted with white.

Skilled predator of small fishes and crustaceans, the Chinese trumpetfish presents a range that includes the tropical and subtropical waters of the Indian and Pacific oceans where it prefers coral reefs environments, up to about 120 m of depth.

Just over 5 cm long, the Pugheaded pipefish (Bulbonaricus brauni) is a sort of anguilliform pipefish who has lost almost all fins and the typical elongated snout of the Syngnathiformes, characters it maintains only at the larval stage, before its demersal life hidden among the polyps of plate-like madrepores.

Just over 5 cm long, the Pugheaded pipefish (Bulbonaricus brauni) is a sort of anguilliform pipefish who has lost almost all fins and the typical elongated snout of the Syngnathiformes, characters it maintains only at the larval stage, before its demersal life hidden among the polyps of plate-like madrepores © Christian Gloor

The Black-striped pipefish (Syngnathus abaster Risso, 1827) has a filiform apperance, quite similar to that of the other membres of the family they belong to (Syngnathidae). Usually the dimensions of the body keep on 15-20 cm of length.

The mouth is very small and opens at the extremity of the short and straight snout marked above by a keel. There is a dorsal fin, low and of equal length in all its developemnt; the caudal fin is small, whilst the anal is very reduced. Usually the livery is of brown or bright green colour, with the mature females presenting vertical streaks on the abdomen.

Strictly coastal species, the Black-striped pipefish is diffused and common in the Atlantic Ocean from the Bay of Biscay to Morocco, in all the Mediterranean and in the Black Sea. Remarkably euryhaline fish, it lives also at the mouth of the rivers and often in their course even for very long distances where it settles with stable populations.

More normal is the look of the Ringed pipefish (Dunckerocampus dactyliophorus), just under 20 cm long, and frequent in tropical Indo-Pacific.

More normal is the look of the Ringed pipefish (Dunckerocampus dactyliophorus), just under 20 cm long, and frequent in tropical Indo-Pacific © Paddy Ryan

Another representative of the Syngnathidae is the Sargassum pipefish (Syngnathus pelagicus Linnaeus, 1758) diffused in a vast range of western Atlantic, from the marine waters of New Scotland up to the Brazilian ones.

It is a fish that reaches a size of about 20 cm or little more that is distinguished by the absence of the pelvic fins. The livery is brownish on the dorsal parts, that in the immature specimens are crossed by 11-13 brown bands. The ventral parts are whitish.

The species owes the name with which is known by the fact that often it is found in open sea among floating masses of Sargassum, a genus of brown alga, where it seems that it feeds on planktonic invertebrates.

The Pugheaded pipefish (Bulbonaricus brauni Dawson et Alle, 1978), known also as Eel pipefish, is a syngnathid of small size, usually about 5 cm.

But not by chance Harlequin ghost pipefish (Solenostomus paradoxus), just over 10 cm long, is defined as paradoxical by the scientific name.

But not by chance Harlequin ghost pipefish (Solenostomus paradoxus), just over 10 cm long, is defined as paradoxical by the scientific name © Bernd-Hoppe

Resembling a small eel, it has a livery of brown-reddish colour dotted with white.

At the adult stage, the Pugheaded pipefishe has a pointed frontal process and has no dorsal and pectoral fins. The species is found among the coral reefs of the eastern Indian Ocean waters.

To the family Sygnatidae belongs also the Ringed pipefish or Banded pipefish (Dunckerocampus dactyliophorus Bleeker, 1853), so called due to the numerous dark rings adorning the body and a dark band crossing the opercula. Long on average just under 20 cm, the Banded pipefish is found usually among the coral reefs, in tide pools and in coastal submerged caves of the Pacific and Indian oceans.

No less surprising is the Blue-finned ghost pipefish (Solenostomus cyanopterus) that may take on any colour, even red, just to blend in with the environment.

No less surprising is the Blue-finned ghost pipefish (Solenostomus cyanopterus) that may take on any colour, even red, just to blend in with the environment © Benoit Lallement

Withe the collective name of pipefishesare known also the Solenostomatidae, family of Syngnathiformes to which are ascribed few species included in the only genus Solenostomus, to which is given also the name of ghost pipefishes, because of their ease of being able to disappear by blending in with algae, gorgonians, arms od starfishes, floating debris, etc. thanks to their remarkable capacity in changing colour and drawings of the body.

The members of the Solenostomatidae distinguish from the other species of the order for the presence of two dorsal fins. Moreover, unlike the Seahorses, in the Solenostomatidae it’s the females who hatch the eggs in a special pouch formed between the abdomen and the well developed pelvic fins.

Similar is the Solenostomus halimeda look. He too, like the previous one, has males much smaller than females and imitates the weeds of the genus Halieda.

Similar is the Solenostomus halimeda look. He too, like the previous one, has males much smaller than females and imitates the weeds of the genus Halieda © Sonja Ooms

The Harlequin ghost pipefish or Ornate ghost pipefish (Solenostomus paradoxus Pallade, 1770), is a fish of just over 10 cm, with the females bigger and wider than the males.

The livery is of a colour varying from black to yellow and red brightened up by dots and stains.

It is a species reported for the western waters of the Pacific and Indian oceans.

The Blue-finned ghost pipefish (Solenostomus cyanopterus Bleeker, 1854) known also with other names, like Racek’s ghost pipefish, or Squaretail ghos-pipefish, is a fish of just over 15 cm whose body shape and the ease of changing colour allow him to merge with a branch of marine phanerogams where he prefers to stay.

The Common seadragon (Phyllopteryx taeniolatus), present between southern Australia and Tasmania, recalls the seahorses but with leafy protuberances.

The Common seadragon (Phyllopteryx taeniolatus), present between southern Australia and Tasmania, recalls the seahorses but with leafy protuberances © Paddy Ryan

Finally, the Halimeda ghost pipefish (Solenostomus halimeda Fritzsche et Randall 2002) in particular characterizes for having the dorsal pelvic and caudal fins little developed and the caudal fin truncated. It is frequent in the coral reef of coastal waters.

The Seadragons are Syngnathiformes of a look very similar to that of the seahorses but with the body particularly rich in mimetic dermal protuberances that confuse it with floating algae. The Seadragons  have a body whose average length is of about 20 cm but that may exceed even 45 cm. These bizarre fishes are diffused in the seas of southern Australia where are reported the species here below mentioned.

The Common seadragon (Phyllopteryx taeniolatus  Lacépède, 1804) is a fish whose average dimensions keep on 45 cm. Similar in the appearance to the Hippocampus, it distinguishes for the presence of leaf-like protuberances with which it blends in with the aquatic plants among which it lives, along the southern coast of Australia.

The Spiny pipehorse (Solegnathus spinosissimus) reaches New Zealand. Has the tail prehensile like the seahorses, but it is more similar to a pipefish.

The Spiny pipehorse (Solegnathus spinosissimus) reaches New Zealand. Has the tail prehensile like the seahorses, but it is more similar to a pipefish © Paddy Ryann

The Spiny seadragon (Solegnathus spinosissimus Günther, 1870), commonly known with other names such as Spiny pipehorse, Banded pipefish and Australian spiny pipehorse is a fish whose average length reaches little less than 50 cm. It lives in the southern Australia and New Zealand waters.

Finally, are to be mentioned the Fistulariidae, family of Fishes Syngnathiformes with a particularly thin and elongated look and having no barbel on the chin unlike other membres of the order. The eyes are big and the snout is elongated with the jaws joined together like a tube. The dorsal and anal fins, small and asymmetrical to each other, and also the ventral fins are moved very far back. The caudal fin is forked and has a long median filament. Over 2 m long, the Fistulariidae stand among the biggest membres of the order. On the body are present small and sporadic tubercles. The livery is usually greenish and can display dark streaks on the back.

The Fistulariidae are greedy predators recalling Aulostomus. The about 1 m Blue spotted cornetfish (Fistularia commersonii) has reached via Suez Canal the Mediterranean.

The Fistulariidae are greedy predators recalling Aulostomus. The about 1 m Blue spotted cornetfish (Fistularia commersonii) has reached via Suez Canal the Mediterranean © Rafi Amar

The family, represented by only one genus in turn fractionated in about 4 species, is present in the tropical waters of all ocans with greater frequency on the hard bottoms and in the coral reefs.

As a consequence of Lessepsian migration, in the Mediterranean has permanently settles the Smooth flutemouth (Fistularia commersonii Rüppel, 1838), Syngnathiformes whose average dimensions usually maintain around the 1 m of length.

Known with the names of Razorfish or Coral shrimpfish (Aeoliscus strigatus Günther, 1861), is a Syngnathiformes that, like the membres of the Centriscidae, family they belong to, distinguishes for having the body protected by a covering of thin and transparent plates that extend beyond the end to the body and over the caudal fin that is equipped with a sharp spine.

Also razorfishes, that move upside down like Aeoliscus strigatus, finally belong, for the characteristic tubular snout, to the order of the Syngnathiformes.

Also razorfishes, that move upside down like Aeoliscus strigatus, finally belong, for the characteristic tubular snout, to the order of the Syngnathiformes © Giuseppe Mazza

Other characteristic, unique within the membres of the order, is that of swimming with the head facing downwards and with the tail upwards.

Averagely 15 cm long, the Razorfish presents a livery that, depending on the habitat, may vary from whitish with a black strip to greenish yellow with a diffused dark band.

It is diffused in the western coastal waters of the Pacific and Indian oceans, where is found among the meadows of marine phanerogams and the coral reefs. It mainly feeds on small invertebrates.

Order Tetraodontiformes

Balistoides conspicillum. The Tetraodontiformes include about 400 species, mostly marine. They have the jaw bones fused in pairs into two plates, similar to teeth.

Balistoides conspicillum. The Tetraodontiformes include about 400 species, mostly marine. They have the jaw bones fused in pairs into two plates, similar to teeth © Giuseppe Mazza

They represent an order of Actinopterygii  where are included species that characterize for having the bones of the jaw similar to teeth, merged in couples in two plates, one upper and one lower, to form a sort of beak, hence the scientific name. Furthermore, in relation to the fact that these fishes nourish mainly of preys having a hard shell, like molluscs and crustaceans, many species are also equipped with pharyngeal teeth. However, it should be noted that, also for this order, not all scholars agree about its systematic position and some consider them a suborder of the Perciformes.

Also the appearance of the Tetraodontiformes is very uncommon and varies from the cube shape of the Boxfishes, to the globular shape of the Pufferfishes and the Porcupinefishes or to the laterally compressed of the Triggerfishes and of the Filefishes. Except for Triggerfishes, the body of these fishes is protected by a rigid armour formed by robust plates or spines or by very hard and coriaceous skin that, however, prevents their lateral bending. Due to the body stiffness, these fishes are able to swim very slowly uniquely under the push of the fins (ostraciform swimming).

The sizes are very variable. The Ocean sunfish (Mola mola) is the largest of the order, with about 3 m of length, and 2 t of weight.

The sizes are very variable. The Ocean sunfish (Mola mola) is the largest of the order, with about 3 m of length, and 2 t of weight © Giuseppe Mazza

The dimensions are very variable, comprised by just 2 cm of the Filefish (Rudarius excelsus Hutchins, 1977) to the Common mola or Ocean sunfish (Mola mola Linnaeus, 1758) that, with about 3 m of length and a weight of more than 2 thousand kg, is one of biggest bony fishes in the world.

In almost all species of the order the fins appear simple, small and rounded. The pelvic fins usually are missing but, in the cases where they are present, they are fused and little visible. The species ascribed to the family of the Molidae have the dorsal and anal fins very high and do not have swim bladder and spines.

Another extraordinary defensive characteristic typical of the Balloonfishes and of the Porcupinefishes is that of being able to swell considerably by inhling large quantities of water through a diverticle of their own stomach. So puffy, these fishes get difficult to swallow even for large predators.

Conversely, the smallest is the Rudarius excelsus, a filefish only 2 cm long.

Conversely, the smallest is the Rudarius excelsus, a filefish only 2 cm long © Kelly-Anne Masterman

Moreover, in most Tetraodontiformes the muscles and the viscera contain a neurotoxin, the tetradotoxin, powerful inhibitor of the repiratory function that causes rapid death.

The Tetraodontiformes include about 400 species and most of them live in marine waters where they prefer the environments associated with the tropical coral reefs, but several species are found in the mouths and in the courses of freshwater.

The systematics of the order is rather controversial especially in its subdivision in families some of which after the opinion of experts are attributed to other order, that of the Perciformes. Here is taken into account the opinion that includes in the Tetraodontiformes about 400 species distributed in 10 families, of some of which we outline the main distinctive features.

Family Monacanthidae – Filefishes

The Scribbled leatherjacket filefish (Aluterus scriptus) that can be 110 cm long, stands among the biggest of the family Monacanthidae.

The Scribbled leatherjacket filefish (Aluterus scriptus) that can be 110 cm long, stands among the biggest of the family Monacanthidae © Paddy Ryan

They are fishes that owe their common name of Filefishes to the particularly rough skin. They form a family whose components characterize for having elongated and slightly rhomboid body, with the head equipped with on the crest one erectile spine. The snout is prolonged and bent like a rostrum.

The Monacanthidae include fishes having no ventral fins, replaced by two spine merged at the abdomen by means of an epidermal membrane. The dorsal fin and the anal one are elongated and the tail is robust. The dimensions are very varied, from few centimetres up to one metre.

Depending on the species, the livery may get a mimetic colouration or showy with spots and stripes. The juvenile forms are characterized by a big snout and by a long tail and with a livery decidedly different from the adults’ one.  Amply diffused in the tropical waters of all oceans, mainly in the Australian seas, the Monacanthidae merge more than 100 species of which of some following we give some distinctive elements.

Oxymonacanthus longirostris, about 12 cm long, is one of the most colourful. To note, on the back, a solid defensive stiletto blockable upright.

Oxymonacanthus longirostris, about 12 cm long, is one of the most colourful. To note, on the back, a solid defensive stiletto blockable upright © François Libert

The Orange filefishes (Aluterus schoepfii  Walbaum, 1972) is a fish that usually reaches 40 cm and even more in length. Benthic fish, is usually found among the vegetation of sandy or muddy bottoms at various depths.

The Scrawled filefish (Aluterus scriptus Hospeck, 1765) is a fish with a very compressed body and of oval elongated shape, with small mouth opening at the extremity of the pointed snout. Called also with the name of Broomtail filefish, this fish can even reach the length of 110 cm.

Animal with strong camouflage abilities, the Scrawled filefish has the body with a background colour that depending on the environmental characteristics may vary from brown to greenish up to white marbled by dark spots and stripes mostly located on the head. It is found in a circumtropical range where it preferably frequents environments with algae and associated with the coral reefs, but also those of lagoons.

Family Balistidae – Triggerfishes

This erectile stiletto, that remains such also in the belly of predators, is the typical defense weapon of Balistidae. Here the Orange-lined triggerfish (Balistapus undulatus).

This erectile stiletto, that remains such also in the belly of predators, is the typical defense weapon of Balistidae. Here the Orange-lined triggerfish (Balistapus undulatus) © Giuseppe Mazza

They form a family whose components are indicated with the collective name of triggerfishes, derived from the Latin term balista, in reference to the particular shape of the fins that evokes that of such deadly weapon. In particular, the trigger of the crossbow is formed by the first of the 3 spiny rays where has transformed the dorsal fin. This ray is erectile and has a sort of safety block formed by the second spiny ray.

The pectoral fins are small but sturdy, instead the ventral ones are completely missing.

Ovoid shaped, strongly compressed laterally, the membres of the Balistidae have a big head with protruding eyes and the mouth forged into a robust beak armed with sharp teeth.

The dimensions of the Balistidae are usually comprised between 30 and 75 of length, depending on the species.

Balistes vetula. With folded fin the Balistes may even enter dens with low door and blocking it raised sleep soundly without being carried out by the currents.

Balistes vetula. With folded fin, Balistes may even enter dens with low door and blocking it raised sleep soundly without being carried out by the currents © Giuseppe Mazza

The Triggerfishes can be esily recognized also because of their characteristic modes obtained swaying alternately left and right the first dorsal and anal fins, placed specularly close to the tail.

The family Balistidae, considered particularly similar to the Filefishes of the Monacanthidae, unites species widespread in the tropical and subtropical waters of the Indian, Pacific and Atlantic oceans and in the temperate ones of the Mediterranean.

Of diurnal habits and highly territorial, the Balistidae  feed mainly on invertebrates, algae and zooplankton.

Of the over 40 species attributed to the family, we mention the following.

The Starry triggerfish (Abalistes stellaris Bloch at Schneider, 1801), called also Flat-tailed triggerfish is the only representative of the genus.

When swimming, however, this stiletto is of no use, and the first dorsal fin often disappears, like in this Balistes capriscus, into a special housing.

When swimming, however, this stiletto is of no use, and the first dorsal fin often disappears, like in this Balistes capriscus, into a special housing © Giuseppe Mazza

Usually about 60 cm long, it is found on muddy bottoms and among the coral reefs of the western waters of the Pacific and Indian oceans and of the Red Sea. Of greyish colour, dotted with white spots, the Starry triggerfish characterizes for the presence of a deep groove in front of the eye.

The Orange-lined triggerfish (Balistapus undulatus  Park, 1797), only member of the genus, has a very lively and multicolored livery. It is found in the coral reefs and in the lagoons of Pacific and Indian oceans atolls.

The Pig-faced or Grey triggerfish (Balistes capriscus Melin, 1789), is a fish that on average reaches 60 cm in length. Diffused in the shallow coastal waters of the Atlantic and of the Pacific, the Grey triggerfish is found usually in the coral reefs.

Another species of the genus is the Variegated triggerfish or Queen triggerfish (Balistes vetula Linnaeus, 1758). This is a Balistidae that may measure up to 50 cm or little more in length that is met in the Atlantic waters.

With its 75 cm of length, the Titan triggerfish (Balistoides viridescens) of tropical Indo-Pacific is the biggest extant Balistidae.

With its 75 cm of length, the Titan triggerfish (Balistoides viridescens) of tropical Indo-Pacific is the biggest extant Balistidae © Gianni Neto

Among the coral reefs of the Pacific and Indian oceans live the Clown triggerfish (Balistoides conspicillum  Bloch et Schneider, 1801) and the Titan triggerfish (Balistoides viridescens Bloch et Schneider, 1801).

Other species of Balistidae of the coral reefs of the Indian and Pacific oceans, are the Black-bodied triggerfish (Odonus niger, Rüppell, 1836), only represenative of the genus, the Yellowmargin triggerfish (Pseudobalistes flavomarginatus Richardson, 1845) and the Yellow-spotted triggerfish (Pseudobalistes fuscus Bloch et Schneider, 1801).

And more, the congeneric species Rectangular triggerfish (Rhinecantus rectangulus Bloch et Schneider, 1801) and the Blackbelly triggerfish (Rhinecantus verrucosus Linnaeus, 1758) are found in the tropical waters of the Pacific, whilst the White-banded triggerfish (Rhinecantus aculeatus Linnaeus 1758) is diffused also in the coastal waters of eastern Atlantic. To the same genus is attributed also the Picasso triggerfish (Rhinecantus assasi Forsskål, 1775) that is found mainly in the Indian Ocean and in the Red Sea.

Family Ostraciidae –  Boxfishes

Ostracion meleagris. The boxfishes have the body protected by a rigid bony armour with openings only for the mouth, the eyes, the gills, the fins and the caudal part.

Ostracion meleagris. Boxfishes have the body protected by a rigid bony armour with openings only for the mouth, the eyes, the gills, the fins and caudal part © Brian Cole

They form a family whose members characterize for having the body protected by a rigid bony covering (carapace) that leaves exposed only the mouth, the eyes, the gill opening, the fins and the tail.

Closely related with the Filefishes (Monacanthidae) and with the Pufferfishes (Tetraodontidae), the members of this family called also with other names like Cowfishes, Trunkfishes and Cofferfishes, are diffused in the oceans and the seas of the tropical belt where they love the shallow bottoms and the coral reefs.

To the Ostraciidae are ascribed slightly more than 20 species of which we mention the following.

The Yellow boxfish (Ostracion cubicus Linnaeus, 1758) is the species type that has given the name to the family. Native to the Indo-Pacific waters and of the Red Sea ones, this fish measures about 45 cm of length.

An armour at times full of defensive spines, like in this unusual Tetrosomus gibbosus with triangular section.

An armour at times full of defensive spines, like in this unusual Tetrosomus gibbosus with triangular section. © Giuseppe Mazza

The Horned boxfish (Lactoria cornuta Linnaeus, 1758), is an about 40 cm long fish known mainly for the central-western Pacific waters, where it is found on the muddy and stony seabeds and among the coral reefs.

The Humpback turretfish (Tetrasomus gibbosus Linnaeus, 1758), so called due to the odd shape of its body, is usually 12-20 cm long. Native to the western Pacific  and Indian Ocean waters, this species through Lessepsian migration has reached the Mediterranean.

Family Tetraodontidae – Pufferfishes

Tetraodontidae are considered a family whose scientific name refers to the characteritic that unites all its membres of having 4 wide teeth that merge to form two crushing plates, one inferior and the other superior.

The puffers, like this Arothron hispidus, instead defend by swelling of water, to appear bigger and to get less graspable by predators.

The puffers, like this Arothron hispidus, instead defend by swelling of water, to appear bigger and to get less graspable by predators © Giuseppe Mazza

The common name of Pufferfishes instead originates from their capacity, if threatened, of swelling remarkably and rapidly the body to a ball gulping  down a lot of water.

This swelling capacity is found also in the Diodontidae Porcupinefishes from which, however, the Tetraodontidae differ already at first sight as having the body covered by tiny spines and not by long long spines.

Diffused in the tropical and subtropical waters of the Atlantic, Pacific and Indian oceans, mainly in marine habitats but also in brackish and fresh waters, the Tetraodontidae include about 200 species.

The Guineafowl puffer (Arothron meleagris Lacépède, 1798) is a fish that may measure about 50 cm in length, with the characteristic livery uniformly black dotted with white of bright yellow.

Skin and entrails are then soaked in tetrodotoxin, a poison that blocks breathing. And if it doesn't die he who eats this Arothron meleagris and will then respect the species.

Skin and entrails are then soaked in tetrodotoxin, a poison that blocks breathing. And if it doesn’t die he who eats this Arothron meleagris and will then respect the species © Giuseppe Mazza

The Spider-eye puffer or Ambon pufferfish (Canthigaster amboinensis Bleeker, 1824), is an about 15 cm long fish that ditinguishes of its polychrome and particularly flashy livery.

The White-spotted puffer (Canthigaster jactator Jenkins, 1901) is a little less than 10 cm long small fish, known for the warm waters of the Hawaiian Archipelago.

The Caribbean sharpnose puffer (Canthigaster rostrata Bloch, 1876) is an about 12 cm long small fish living in the central-western Atlantic waters.

Family Diodontidae – Porcupinefishes

To these valid defenses the porcupine fishes add also, swelling like Duodon liturosus, even a spiny look.

To these valid defenses the porcupine fishes add also, swelling like Duodon liturosus, even a spiny look © Giuseppe Mazza

They represent a family of the Tetraodontiformes whose membres are commonly indicated with the term of Porcupinefishes.

Such name gets origin from the fact that their main feature is represented by their capacity in swelling rapidly by swallowing water like the Pufferfishes, but unlike these they have the body bristling with long corneous spines.

The Diodontidae are diffused in the tropical and subtropical water of all the oceans where they are represented by fishes whose dimensions are included between 30 and 90 cm in length.

They gather together about 20 species some of which are here below mentioned.

And in some species, like Chilomycterus antillarum, the spines stay always erect, with triangular base, regularly spaced from each other.

And in some species, like Chilomycterus antillarum, the spines stay always erect, with triangular base, regularly spaced from each other © Kevin Bryant

The Web burrfish (Chilomycterus antillarum Jordan et Rutter, 1897), also called Spiny box puffer or Striped burrfish, is an about 30 cm Diodontidae, native to the western Atlantic.

The Freckled porcupinefish or Porcupine pufferfish (Diodon holocanthus Linnaeus, 1758) can approximately reach the 50 cm and is found in the coral reefs of the tropical waters of all the oceans.

The Slender-spined porcupinefish or Globe fish (Diodon nicthemerus Cuvier, 1818) is an about 40 cm long fish living in the southern Australian waters.

Family Molidae – Molids

To the family of the molas, with the circular body reminding a millstone, belong about 5 species. Here Mola alexandrini with even 3 m of diameter.

To the family of the molas, with the circular body reminding a millstone, belong about 5 species. Here Mola alexandrini with even 3 m of diameter © Simon Pierce

So called due to tthe circular shape of the body that recalls the millstone, from the Latin “mola,” the Molidae form a

family of Tetraodontiformes very particular due to several distinctive characters. Besides standing among the biggest Teleostei Fishes, the Molidae distinguish because they don’t have caudal bones, have the skeletal structure mostly made of cartilage and are devoid of bony plates on the skin.

Another characteristic of the Molidae is that of swimming mainly utilizing the dorsal and anal fins. It is assumed that the pectoral fins have the function of stabilizers.

Pelagic fishes, the Molidae are very bad swimmers and usually stay close to the surface and let themselves to be carried by the currents. Present in all seas, they include about 5 species with among them the Ocean sunfish (Mola mola Linnaeus, 1758).

Order Zeiformes

The Saint Pierre (Zeus faber) so called because of the drawing of a coin on the sides recalling an evangelical episode (Matthews 17.24-27) belongs to the Zeiformes

The Saint Pierre (Zeus faber) so called because of the drawing of a coin on the sides recalling an evangelical episode (Matthews 17.24-27) belongs to the Zeiformes © Pierre Corbrion

They are an order of the Actinopterygii where are included species that mainly caracterize for the particular shape of the mouth that can be prolonged by extending like a tube for catching the preys. Variable in appearance and size, the Zeiformes have the body tal and very compressed laterally, sometimes covered by spiny bone plate. The swim bladder is present. The fins have numerous spiny rays. In some members of the family Zeidae, the dorsal fin has elongated rays, at times filiform. The dimensions vary from few centimetres, 7-15 of the Zenionidae, to about 90 cm of the St. Pierre (Zeus faber Linnaeus, 1758).

The Zeiformes include species, all marine, living in various environments, often even at remarkable depths. Some species have particularly meats. The St. Pierre is a species diffused in tropical and temperate waters, including the Mediterraean and the Black Sea, where it prefers the environments with sandy or muddy mobile seabeds, at depths usually between 50 to 400 m.

Order Clupeiformes

School of European pilchards (Sardina pilchardus). They belong to the order of Clupeiformes, group of fishes important for human nutrition.

School of European pilchards (Sardina pilchardus). They belong to the order of Clupeiformes, group of fishes important for human nutrition © Roberto Pillon

Order of the Actinopterygii  to which are attributed species with tapered body, more or less tall and compressed laterally, covered with scales except for the head.

The membres of the order have a non-protractile mouth and the fins do not have spiny rays and the caudal has always two lobes.

The lateral line is present only on the head. The Clupeiformes are physostomes fishes, having the swim bladder connected with the gut by means of the pneumatic duct. To the order belong numerous species amply diffused in the seas and in freshwaters where they are elements of considerable importance of the trophic networks as form the main source of food of several predators.

Several species of Clupeiformes, such as anchovies, sardines, herrings and others more, of fundamental importance in human nutrition, have meats with a significant concentration of vitamins and minerals  and are particularly rich in omega 3 and other unsaturated fats.

This unusual close-up of Clupea pallasii, evoking the existential drama of modern men portrayed in the famous painting "The Scream" by E. Munch, seems to remind that the sad destiny of all Clupeiformes is that to be preyed.

This unusual close-up of Clupea pallasii, evoking the existential drama of modern men portrayed in the famous painting “The Scream” by E. Munch, seems to remind that the sad destiny of all Clupeiformes is that to be preyed © Alex Heymanl

United by these nutritional characteristics with the generic commercial name of “blue fish” to other species of other orders, in particular that of the Perciformes, the Clupeiformes  also figure among the main components of the trophic network of the oceans of the whole world.

In fact, they form a main source of food for several predators, not only fishes (tuna, sharks, swordfishes and others), but also cetaceans (whales, dolphins and others), pinnipeds (seals, sea lions, fur seals), marine birds, such as penguins, cormorants, pelicans.

Here below we furnish the essential elements characterizing the most known species of the Clupeiformes  and we refer you for further information to the specific data sheets.

The European pilchard (Sardina pilchardus Walbaum, 1792), the only species of the genus, recalls in the appearance the anchovy from which however it’s easy to distinguish as having taller body and more compressed laterally, covered of big scales that come off easily upon contact.

And more, the European pilchard has pointed head with big eyes covered by a fatty eyelid that reminds that of the Twait shad (Alosa fallax Linnaeus, 1803).

The mouth is big and facing up, with the mandible longer than the jaw, and equipped with small teeth.

On the ventral parts, the European pilchard displays a row of sharp scales (Scutelli) that, unlike European sprat (Sprattus sprattus Linnaeus, 1758), do not form a real keel.

The gill opercula are equipped with bony keels arranged in a fan shape. The livery is light blue or greenish iridescent on the dorsal parts, slivery on the sides with small black spots, whitish on the ventral ones.

Usually 15-20 cm long, this fish ay even reach the length of 30 cm. Pelagic fish that usually lives in open waters, during the good season, the European pilchers reaches also shallow and coastal waters.

The reproduction occurs during the whole year, with a top during the winter time. Highly productive, each female of the European pilchard lays a big quantity of pelagic eggs that hatch after some days. The larvae shortly assume a livery similar to those of the adults.

Here an entire school of Engraulis mordax is preyed upon by a Humpback whale (Megaptera novaeangliae.

Here an entire school of Engraulis mordax is preyed upon by a Humpback whale (Megaptera novaeangliae © Donna Pomeroy

Of significant economic importance, the European pilchard is subject to particularly marked overfishing with consequent strong reduction in fish stocks.

The Round sardinella (Sardinella aurita Valenciennes, 1847) is a species looking a lot to the European pilchard from which differs due to the stockier shape and the presence of a noticeable golden coloured line on the sides.

It is a pelagic species, whose range includes the Atlantic Ocean and the Mediterranean Sea where can be found at various depths.

Another species occupying a place of absolute importance in the human economy is the European anchovy or Alice in Italian (Engraulis encrasicolus Linnaeus, 1758), fish that at first glance may be mistaken with the European pilchard from which is easy to distinguish because of a whole series of characters.

Here it's a Glaucous-winged gull (Larus glaucescens) who takes advantage without moderation of a school in surface of Clupea Pallaslii.

Here it’s a Glaucous-winged gull (Larus glaucescens) who takes advantage without moderation of a school in surface of Clupea Pallaslii © Liam Ragan

The European anchovy has tapered and slender body, long on average 15-18 cm, and ventrally devoid of the crest of rigid scales present in the European pilchard.

The head is conical and presents the big eyes and placed well in front. The mouth is very big, with the jaw longer than the mandible and is equipped with several small teeth. The body is blue-green on the back, silvery, frequently with a dark band on the sides, whitish on the ventral parts.

The European anchovy is a typical pelagic fish that is found also in open seas and that in May-June gets close to the coasts for the reproduction. Moderately euryhaline species, tolerates also the brackish waters and not infrequently enters the mouths and the lagoons. It’s one of the few species that from the Mediterranean can move to the Red Sea, thus making a journey contrary to that of the Lessepsian migrants.

And this Fish hawk (Pandion haliaetus) carries happily to its "dining room" a Brevoorthia tyrannus, a Clupeiformes that may exceed the 30 cm of length.

And this Fish hawk (Pandion haliaetus) carries happily to its “dining room” a Brevoorthia tyrannus, a Clupeiformes that may exceed the 30 cm of length © Sean Werle

Other species indicated with the common name of Anchovy to which however they resemble, are the Pacific anchovy (Engraulis ringens Jenyns, 1842), also called Chilean anchovy or Peruvian anchovy, that is one of the most commercially caught fish species, and the Indian anchovy (Stolephorus indicus van Hasselt, 1823), known also as Hardenberg’s anchovy, a widely consumed species in the cuisine of the maritime regions of south-east Asia.

Other species of Clupeiformes of great importance for the commercial fishing and the economy of northern Europe, is the Atlantic herring (Clupea harengus Linnaeus, 1758), fish populating the coastal waters of northern Atlantic. It is completely absent in the Mediterranean Sea.

Its is a fusiform fish, laterally compressed, covered with small scales that ventrally form a weak keel.

The Atlantic herring (Clupea harengus), of same size, is much fished for human consumption on both coasts of north Atlantic.

The Atlantic herring (Clupea harengus), of same size, is much fished for human consumption on both coasts of north Atlantic © hunterefs

Typically, the gill opercula are smooth with rounded back margin. The mouth, pointed and equipped with tiny teeth, has the mandible protruding well beyond the jaw. The dimensions of the Herring usually maintain on 30 cm, even if some specimen may reach the length of 50 cm. The colour of the body is uniformly blue with greenish shades on the back and white-silvery on the sides and on the ventral parts.

The Herring is a pelagic fish living united in numerous groups that frequently form great schools, whose main food is represented by small codepod crustaceans. In turn, the Herring is an important source of food for several predators.

Fishes, on particular sharks, rays, salmons, cods. Mammals, such as dolphins, orcas and porpoises, big birds, especially ducks (Mergansers, Boobies, Tufted ducks) stand among the main predators of the Herring. During the time of the reproduction, this fish leaves the open seas waters and migrates in the coastal ones. The females spawn alarge number of non-pelagic eggs in zones with pebbly seabeds.

The Round sardinella (Sardinella aurita) very similar to Sardine; distinguishes for the stockier shape and the golden line on sides.

The Round sardinella (Sardinella aurita) very similar to Sardine; distinguishes for the stockier shape and the golden line on sides © Allison & Carlos Estape

With the collective name of Alosa  are known the more than 25 species included in the homonymous genus that characterize for the absence of teeth on the palate, on the vomer and on the tongue. These are species hose dimensions usually do not exceed the length of 40-50 cm. Almost all marine, the Alosa in spring ascend the rivers for the reproduction.

Alosa alosa (Linnaeus, 1758) is an eastern Atlantic species similar to the Twait shad from which distinguishes already at first sight as having only one black spot behind the opercula.

The Agone (Alosa agone  Scopoli, 1786), stands among the few species of the genus that constantly lives in fresh waters. Reported for various pre-alpine lakes of North Italy, the Agone has usually smaller dimensions than the other species of the genus and is very appreciated as food.

Even 50 cm long, the Twaite shad (Alosa fallax) is fished in the eastern waters of Atlantic and in the western ones of Mediterranean and of Black Sea.

Even 50 cm long, the Twaite shad (Alosa fallax) is fished in the eastern waters of Atlantic and in the western ones of Mediterranean and of Black Sea © Hans Hillewaert

The European sprat or Papalina (Sprattus sprattus Linnaeus, 1758) is a species of Clupeiformes very similar to the European pilchard from which easily distinguishes for the ventral fins planted more anteriorly, at the same height of the dorsal fin as well as for the presence of a robust ventral crest formed by hard scales. Moreover, the European sprat has the body not exceeding the length of 15 cm and a livery of bright blue colour on the dorsal parts and silvery white on the ventral ones. This species is diffused in a vast range including the northern marine waters. The European sprat is quite rare in the Mediterranean.

The Twait shad (Alosa fallax Linnaeus, 1803) is a fish having the body of oval shape and compressed laterally, that in the adults averagely reaches the dimensions of 35-50 cm. The species characterizes for having an adipose membrane, thick and transparent, that covers the eyes and the opercula marked by radial straks. The ventral keel is formed by bony shields with a spine facing backwards. The Twait shad is found in the eastern waters of the Atlantic, in the western ones of the Mediterranean and of Black Sea.

Order Aulopiformes

To the order of Aulopiformes belong demersal fishes appeared in the Miocene and mostly extinct. Here a Sand diver, a known lizardfish.

To the order of Aulopiformes belong demersal fishes appeared in the Miocene and mostly extinct. Here a Sand diver, a known lizardfish © Brian-Cole

Called also Alepisauriformes, they are considered an almost completely extinct order of Fishes Actinopterygii whose taxonomic composition is not clearly defined.

Many of the Aulopiformes are deep sea fishes and their biology is poorly known. Some species have characters of hermaphroditism, even autogamous.

By the way, according to the opinion of some scholars, a very controversal opinion anyway, this order is nowadays represented only by the speceis of Synodus (Scopoli, 1777). To further complicate the situation, also the attribution of the genus Synodus to the Aulopiformes is in any case also discussed. However, leaving apart taxonomic dissertations, among the species arributed to the order, the following are to be mentioned.

It is often found buried while tending ambushes on the seabeds of tropical Atlantic. Here, in Florida, has just seized a Bothus ocellatus.

It is often found buried while tending ambushes on the seabeds of tropical Atlantic. Here, in Florida, has just seized a Bothus ocellatus © Mickey Charteris

In the genus Synodus are included small and medium sized species, with fusiform body and mouth wide and provided with several teeth of various shape that are implanted even on the mouth. The livery is varied and in some tropical forms is lively coloured.

The genus is amply diffused in the tropical and subtropical seas where is met in coastal environments with shallow waters, espcially rocky, and of the coral reefs. This is the case in the Caribbean of Synodus intermedius (Spix & Agassiz 1829).

In the Mediterranean waters the genus is present with the Atlantic lizardfish (Synodus saurus Linnaeus, 1758). This is a small fish, usually less than 20 cm long, with very big mouth provided with numerous sharp teeth od various size. The livery of the Atlantic lizardfish has a colouration varying from grey to brown on the dorsal parts, whitish on the lateral ones; on the sides adorned by blue or clear vertical stripes on the sides.

Latropiscis purpurissatus is an Aulopiformes endemic to the Australian coasts. Called Sergeant baker, it belongs to the flagfins.

Latropiscis purpurissatus is an Aulopiformes endemic to the Australian coasts. Called Sergeant baker, it belongs to the flagfins © Sascha Schulz

To the Aulopiformes various scholars attribute also the genus Aulopus whose most known membre  is the Yellowfin aulopus or Royal flagfin (Aulopus filamentosus Bloch, 1792), medium sized fish, usually about 40 cm, present in the eastern Atlantic and Mediterranean waters.

Other species of the genus are Aulopus bajacali (Parin & Kotlyar, 1984) and Aulopus chirichignoae (Béarez et al., 2024), both known as Eastern Pacific flagfin. Very similar in the appearance and often confused with each other, they are about 30 cm long fishes living on the muddy and sandy seabeds of the continental shelf of eastern Pacific.

Finally, is to be remembered the Sergeant Baker (Latropiscis purpurissatus J. Richardson, 1843), fish of the group Flagfin, about 60 cm and endemic of the Australian seas.

Order Abuliformes

The Abuliformes include just over ten species. The most common, Albula vulpes, may reach the length of 1 m per a weight of 10 kg.

The Abuliformes include just over ten species. The most common, Albula vulpes, may reach the length of 1 m per a weight of 10 kg. © Kevin Bryant

Considered an order of Actinopterygii to which are attributed species having elongated body with conical head and elongates snout where on the lower part opens the rather small mouth. The fins present only soft rays and the caudal fin conspicuously forked. The dimensions may even reach the length of 1 m per a weight of about 10 kg.

Diffused in all tropical seas, where they populate the coastal environments with shallow waters and sandy and muddy seabeds, the Abuliformes include just over ten species, among which the most common is the Bonefish

(Albula vulpes Linnaeus, 1758). The colour of the body is silvery and is marked by longitudinal dark lines with dark longitudinal lines similar to those of the Flathead grey mullet  (Mugil cephalus Linnaeus, 1758). The Bonefish is a euryhaline species diffused in the American marine waters, where it prefers the coastal environments.

Order Anguilliformes

The Anguilliformes include fishes similar to snakes, like this Ophichthus ophis, and lengths between 30 cm and 3 m.

The Anguilliformes include fishes similar to snakes, like this Ophichthus ophis, and lengths between 30 cm and 3 m © Gustavo F. de Carvalho-Souza

Considered an order of Fishes Actinopterygii, the Anguilliformes unite species that characterize for the elongated look, that is somewhat reminiscent of a snake.

The dimensions vary depending on the species, including those of about thirty centimeters of the Thinlip conger up to 3 m of the European conger.

Most Anguilliformes don’t have ventral fins and have the dorsal and the anal fins very long. Conversely, the pectoral fins are small and rounded.

The livery of the species of the order is fairly varied, in most species it gets a uniform dark colouration with which these fishes blend in with the muddy environment where they are used to live.

They are sea fishes, excepting the species of the genus Anguilla, that live in freshwater but then reach the sea to reproduce like this Anguilla anguilla.

They are sea fishes, excepting the species of the genus Anguilla, that live in freshwater but then reach the sea to reproduce like this Anguilla anguilla © Giuseppe Mazza

In other species the livery presents a clear colouration and adorned with dark spots and dotslike in the Spotted snake eel (Ophichthus ophis Linnaeus, 1758) or in the Saddled snake eel or in the Miro leopard (Pisodonophis semicinctus Richardson, 1848).

To the Anguilliformes belong species mainly diffused in marine environment. Only the species of the genus Anguilla live in fresh waters and migrate in the sea at the time of the reproduction. The Eel or  European eel (Anguilla anguilla  Linnaeus, 1758) is a teleost fish of the family Anguillidae. From the eggs of the Anguilliformes hatch into particular leaf-like larval forms called leptocephali.

Of the many species included in the order, here we barely dwell on the few that, regularly or more or less accidentally, are found also in the Mediterranean waters.

The larvae of the Anguilliformes have all the look of a transparent willow leaf and are called leptocephali.

The larvae of the Anguilliformes have all the look of a transparent willow leaf and are called leptocephali © Gonzalo Mucientes Sandoval

Various species are included in the Congridae, family whose components are known with the names of Congers and of Garden eels.

The above mentioned European conger (Conger conger Linnaeus, 1758) is the giant of the order  and can reach even the 3 metres in length and 70 kg in weight.

Very common in the Mediterranean at various depths, is diffused also in the eastern Atlantic and, accidentally, also in western Black Sea.

The Balearic conger (Ariosoma balearicum Delaroche, 1809) is a small species, up to 50 cm long, amply diffused in the waters of the Atlantic and Indian oceans, of the Red Sea and of the Mediterranean.

The European conger (Conger conger) frequent in Mediterranean and in east Atlantic, is the giant of the order with 3 m of length and 70 kg of weight.

The European conger (Conger conger) frequent in Mediterranean and in east Atlantic, is the giant of the order with 3 m of length and 70 kg of weight © Tamsyn Mann

The already previously mentioned Thinlip conger (Gnathophis mystax Delaroche, 1809) is a small Anguilliformes Congridae usually about 30 cm long that characterizes for having the pointed and protruding snout and very big eyes.

It is a fish common in the Mediterranean waters and in those of central-eastern Atlantic where is found on muddy bottoms usually at depths between 100 and 800 metres.

Always of the Congridae  is the Rhynchoconger trewavasae (Ben-Tuvia, 1993) diffused in deep waters of western Indian Ocean. It is an Anguilliformes of medium size, about 50 cm, whose biology is little known and of which has been found only one specimen in Mediterranean waters.

The Bandtooth conger (Ariosoma balearicum), amply spread in the Atlantic, Indian, Red Sea and Mediterranean, instead, does not exceed the 50 cm.

The Bandtooth conger (Ariosoma balearicum), amply spread in the Atlantic, Indian, Red Sea and Mediterranean, instead, does not exceed the 50 cm © Luis Pérez Berrocal

To another family, that of the Muraenesocidae, belongs the Guinean pike conger or Pontic Chinese (Cynoponticus ferox Costa, 1846). Very similar in appearance to the Conger eel, the Pontic Chinese has a body reaching even the length of 2 m, of brown red colour on the back with dark grey sides and ventral parts. The fins are edged in black, but the pectoral ones that are completely black.

Present in eastern Atlantic, the Pontic Chinese is one of the few membres of the genus living also in the Mediterranean where it seems to be relegated in western waters. Usually it is found over sandy seabeds where it preys mainly on crustaceans and fishes.

To the Muraenesocidae is ascribed also the Daggertooth pike conger (Muraenesox cinereus (Forsskål, 1775), species widely diffused in the Pacific and Indian oceans of which is reported the finding of some specimen arrived in the eastern Mediterranean waters after a Lessepsian migration.

Similar dimensions have the thin Brown garden eels (Heteroconger longissimus) that emerge from the Atlantic seabeds like stems moved by the wind.

Similar dimensions have the thin Brown garden eels (Heteroconger longissimus) that emerge from the Atlantic seabeds like stems moved by the wind © Pascal Girard

Known also with the name of Darkfin pike eel, this is a fish whose dimensions keep usually on the 80 cm of length, but that may reach, and exceed, even the 2 m. The livery assumes tones varying from grey with the odd fins edged in dark.

Among the Anguilliformes that accidentally can be found also in the Mediterranean waters, are to be mentioned the here below cited species of Ophichthidae, family whose membres are commonly known with the  names of Worm eels of Snake eels.

The Spotted snake eel (Ophichthus ophis Linnaeus, 1758), native to the Atlantic waters, is a fish whose dimensions usually maintain around 1 m, but that can exceed even the length of 2 m.

On mobile or sandy bottoms, at 100-300 m of depth, stands also the Serpent eel (Ophisurus serpens) in east Atlantic and west Indian oceans and in Mediterranean.

On mobile or sandy bottoms, at 100-300 m of depth, stands also the Serpent eel (Ophisurus serpens) in east Atlantic and west Indian oceans and in Mediterranean © josepvilanova

The body is of pale yellow colour, darker or orange on the dorsal parts, adorned with brown spots of variable size. The presence in the Mediterranean of this species is still to be confirmed.

Another component of the Ophichthidae is the Banded snake eel or Culverin (Laiuranus semicicntus Lay et Bennet,1839), is a fish that can be almost 70 cm long. The species distinguishes at first sight for the livery that characterizes for the presence of dark semicircular bands all over its body whose background colour is uniformly whitish. The tail is pointed and rigid. It lives in cliffs and lagoons of tropical waters of the Indian and Pacific oceans.

The Sand snake-eel or Serpent eel (Ophisurus serpens Linnaeus, 1758) is an  Ophichthidae that is found on mobile or sandy seabeds from 100 to 300 m of depth, of eastern Atlantic, western Indian Ocean and also of western Mediterranean.

In tropical Indo-Pacific, from Africa to Hawaii, stands also the Saddled snake-eel (Leiuranus semicinctus) that is just over 60 cm.

In tropical Indo-Pacific, from Africa to Hawaii, stands also the Saddled snake-eel (Leiuranus semicinctus) that is just over 60 cm © Claire Goiran

This is an Anguilliformes with a particularly thin body that may be even 250 cm long.

The livery has a green-grey colouration on the back, silvery on the belly.

Also the Saddled snake eel (Pisodonophis semicinctus Richardson, 1848) is a species of Ophichthidae of eastern Atlantic that has come from the Red Sea into the Mediterranean where it is however rare.

It is a medium-length Anguilliformes, usually 80 cm, that characterizes for a livery of yellowish grey colour with circular black spots on the back and dotted dark on the head.

The morays, frequent in all seas, distinguish easily from the eels because of the absence of the pectoral fins. Here Muraena clepsydra and Gymnomuraena zebra.

The morays, frequent in all seas, distinguish easily from the eels because of the absence of the pectoral fins. Here Muraena clepsydra and Gymnomuraena zebra © Allison & Carlos Estape

With the name of Moray eels are indicated the species of Anguilliformes included in the Muraenidae, family diffused mainly in the tropical and temperate seas. The Moray eels are very common especially in the coral reefs usually at low depth on hard bottoms.

In the Mediterranean waters we find the Mediterranean moray (Muraena helena Linnaeus, 1758) and, less frequently, the Brown moray eel or Monk moray eel (Gymnothorax unicolor Delaroche, 1829). Every now and then is reported the accidental presence of some species that from the Red Sea enters the Mediterranean.

Among the species diffused in western Atlantc we mention 3 species of the same genus, the Green moray (Gymnothorax funebris Ranzani, 1829) and the Goldentail moray (Gymnothorax miliaris Caup, 1856) and the Gymnothorax moringa Cuvier, 1829). Much more numerous are the Morays living in the tropical waters of the coral reefs of the Indian and Pacific oceans.

However not all of them look scary. The colourful Ribbon moray (Rhinomuraena quaesita)of tropical Indo-Pacific amazes with its funny nasal expansions.

However not all of them look scary. The colourful Ribbon moray (Rhinomuraena quaesita)of tropical Indo-Pacific amazes with its funny nasal expansions © Francois Liber

Here we mention the Snowflake moray (Echidna nebulosa Ahi, 1789), the Zebra moray (Gymnomuraena zebra Shaw, 1797) and the Tessellate moray (Gymnothorax favagineus Bloch and Schneider, 1801).

Let us close this quick overview on the tropical Muraenidae with other species of the genus Gymnothorax, such as the Geometric moray (Gymnothorax griseus Lacépède, 1823), the Spotted moray eel (Gymnothorax isingteena Richardson, 1845) and the Giant moray (Gymnothorax javanicus  Bleeker, 1859), rightly the giant of the family with a length of 3 m and a weight of 30 kg.

Singular for the particularly compressed shape are the Ribbon eel (Rhinomuraena quaesita Garman, 1888), an Anguilliformes of more than 1 m in length living in the coral reefs and in lagoons of atolls of the Indian and Pacific oceans and the White ribbon eel (Pseudechidna brummeri Bleeker, 1858), usually 30-70 cm long, known for the waters of the Indo-Pacific.

Order Elopiformes

The Elopiformes have leptocephalus larvae like the Anguilliformes but evoke herrings at first sight. The Tarpon (Megalops atlanticus) may reach 2,5 m and 160 kg.

The Elopiformes have leptocephalus larvae like the Anguilliformes but evoke herrings at first sight. The Tarpon (Megalops atlanticus) may reach 2,5 m and 160 kg © Wolfram Sander

Considered an order of Actinopterygii, the Elopiformes include medium and large sized fishes with not protruding snout and apical or superior mouth that characterizes for the presence of well developed gular plates. The jaw extends beyond the eye. The gill openings are ample. Typically, the caudal fin is deeply forked.

At first sight the Elopiformes recall the Herrings but the presence of leptocephalic larvae denotes their affinity with the Anguilliformes. The order of the Elopiformes is diffused in the tropical seas where it is represented by species living in coastal waters but that can go further also in brackish and fresh waters.

Of the order is to be remembered the Atlantic tarpon (Megalops atlanticus Valenciennes, 1847), fish that can reach the length of 2,5 m and weigh even 160 kg. Referring to the livery of blue-greenish colour on the back with silvery sides, this fish is also called Silver king.

Order Notacanthiformes

Also Notacanthiformes have leptocephalus larvae. They live in deep waters, like Halosaurus pectoralis that may reach the 1200 m, but other species go down to 5.000 m.

Also Notacanthiformes have leptocephalus larvae. They live in deep waters, like Halosaurus pectoralis that may reach the 1200 m, but other species go down to 5.000 m © Ken Graham

The  Notacanthiformes  represent an order of Actinopterygii to which are ascribed species with elongated body, rounded and protruding snout with small and ventral mouth, placed below the eyes.

Due to the presence of a leptocephalic larva, the Notacanthiformes are considered as similar to the Anguilliformes.

Widely diffused in all seas, the order is represented by species living in depths varying from 100 to 5.000 m.

Within the few species of the Notacanthiformes found also in the Mediterranean waters, are to be remembered the following.

The Shortfin spiny eel (Notacanthus bonaparte Risso, 1840), is a modest-sized fish, little less than 30 cm long with body brownish yellow on the back, silvery on the sides and with blue belly. It is reported in the eastern Atlantic waters as  well as in the western Mediterranean ones.

The Pelican eel (Eurypharynx pelecanoides) about 2 m long with a huge mouth, belongs to the Saccopharyngiformes, abyssal fishes too, with leptocephalus larvae.

The Pelican eel (Eurypharynx pelecanoides) about 2 m long with a huge mouth, belongs to the Saccopharyngiformes, abyssal fishes too, with leptocephalus larvae © Gonzalo Mucientes Sandoval

The Shortspine tapirfish (Polyacanthonotus rissoanus De Filippi and Vérany, 1857), is a fish usually less than 20 cm long, that is found in all the Atlantic and in the Mediterranean.

The Oven’s halosaur (Halosaurus owenii Johnson, 1864), is a Notacanthiformes little reported for western Mediterranean. The Oven’s holosaur is an about 50 cm long fish, with the dorsal parts of the body of dark pinkish colour with metallic reflections.

Order Saccopharyngiformes

The Saccopharyngiformes form an order of Actinopterygii to which are ascribed species of various appearance that characterize for the very elongated jaws, excepting the membres of the family in the Monognathidae that do not have the jaw. Another characteristic of the order is the absence of scales, swim bladder, of the ventral fins and in many species also the caudal fin. In the species where it is present, the caudal fin is rudimental.

Kingfish (Lampris guttatus) is a pelagic Lampridiformes that may reach the length of 2 m. Vastly diffused in all seas, is found also in the Mediterranean.

Kingfish (Lampris guttatus) is a pelagic Lampridiformes that may reach the length of 2 m. Vastly diffused in all seas, is found also in the Mediterranean © Giuseppe Mazza

Similar to the Anguilliformes for the presence of a leptocephalic larva, the Saccopharyngiformes are abyssal fishes that are found in all the seas but the Mediterranean. The biology of these fishes is little known. Of the species of the order we recall the following.

The Gulper eel (Saccopharynx ampullaceus Cuvier, 1829), is a fish that can reach the length of 1,5 m, reported in the Atlantic even at 3.000 m of depth.

The Pelican eel (Eurypharynx pelecanoides Vaillant, 1882), just under 2 m long, owes its own name to the huge mouth capable of an incredible opening, hence the common name, that utilizes for collecting the small preys it feeds on. The Pelican eel is diffused in all tropical and temperate seas, Mediterranean excluded.

Order Lampridiformes

Considered an order of Actinopterygii, the Lampridiformes, called also Lampriformes or Allotriognati, they owe their own scientific name to the livery typically coloured in a bright way of its membres.

Frequent in Paleocene, the Lampridiformes count now only a twenty pelagic or abyssal species. With only 30 cm the Metavelifer multiradiatus stands allo,ngst the smallest.

Frequent in Paleocene, the Lampridiformes count now only a twenty pelagic or abyssal species. With only 30 cm the Metavelifer multiradiatus stands allo,ngst the smallest © J. Martin Crossley

The Lampridiformes unite species of very varied look, with the body laterally compressed, mainly very elongated.

Also the dimensions are very variable, from less than 30 cm of the Spinyfin velifer (Metavelifer multiradiatus  Regan, 1907) to the more than 15 m of the Giant oarfish (Regalecus glesne  Ascanio, 1772).

Similarly to many Cephalopod Mollusks, the present Lampridiformes are equipped with an ink pocket that opens in the cloaca with which they can produce a black cloud to escape potential predators.

Already widely represented in the Paleocene, more than 60 million of years ago, nowadays the Lampridiformes   are represented by about twenty pelagic and abyssal species.

The Unicornfish (Lophotus capellei Temminck and Schlegel, 1845) is so called due to a crest formed by the dorsal fin that protrudes from the snout.

Conversely, present in all seas, Regalecus glesne is the giant of the order with a length of 15 m.

Conversely, present in all seas, Regalecus glesne is the giant of the order with a length of 15 m © Thomas Menut

Known also with the name of North Pacific crestfish, it reaches the length of 2 m and lives in the tropical and subtropical waters of the Atlantic and Pacific waters.

The Regalecus (Regalecus glesne Ascanio, 1772), known also with the name of Giant oarfish stands among the biggest extant fishes. It is widespread throughout all seas, including the Mediterranean where is, however, rare.

The Moonfish of Kingfish (Lampris guttatus Brünich, 1788), indicated also with the names of Opah, Cravo, Jerusalem haddock, is a fish whose dimensions may reach the length of 2 m. It is a pelagic fish widely diffused in all seas, Mediterranean included.

The King-of-the-salmon (Trachipterus altivelis Kner, 1859) is a fish that can reach also the dimensions of 180 cm in length living in eastern Pacific waters.

Order Characiformes

The Characiformes include several freshwater species. With about 120 cm of length the terrifying Hdrocynus goliath is the biggest.

The Characiformes include several freshwater species. With about 120 cm of length the terrifying Hdrocynus goliath is the biggest © Gwili Gibbon

They are considered an order of Actinopterygii where are included several freshwater species.

At first sight the species of the order are similar in the appearance to the analogous Cypriniformes,  but they differ from them because of the presence of one short fleshy adipose fin located between the dorsal fin and the tail.

The dimensions of the Characiformesa vary from little less than 2 cm of length of Xenurobrycon polyancistrus    (S.H.Weitzman, 1987) to the 120 cm of the Goliath tigerfish (Hydrocynus goliath Boulenger, 1898).

Many species present the body brightly coloured. To the Characiformes  are attributed several hundred of species diffused in the freshwaters of central and southern America and of Africa.

Thanks to the beauty of the livery and the ease of breeding, several species are frequent guests of the aquaria. Particularly sought after by the aquarists are the so-called Tetra neon fishes, collective term that unites Characiformes with their bright livery and with the square-shaped fins.

Frequent in domestic aquaria, the Cardinal tetra (Paracheirodon axelrodi) who reaches at most the 2,5 cm stands among the smallest.

Frequent in domestic aquaria, the Cardinal tetra (Paracheirodon axelrodi) who reaches at most the 2,5 cm stands among the smallest © Giuseppe Mazza

Here we limit ourselves for a fast overview on the most known and most representative forms of the order, referring to the individual specific sheets for any further information.

The Neon tetra (Paracheirodon innesi Myers, 1936) is a small Tetra fish, on average just over 2 cm long, native to the catchment basin of the Amazon River. Due to its colours, its robustness and liveliness, the Neon tetra is one of the most popular aquarium fishes. The analogous Cardinal tetra (Paracheirodon axelrodi (Schultz, 1956)) lives in the Orinoco and Rio Negro tributaries.

The Payara (Hydrolycus scomberoides G. Cuvier, 1819) is a Tetra fish whose most obvious characteristic is represented by long fang-like teeth protruding from the mandible for 10-15 cm.

The Payara is more than 1 m long Characiformes with a weight of more than 15 kg, living in the waters of the Amazon River basin where it preys on small fishes.

The Giant tigerfish (Hydrocynus goliath Boulenger, 1898), known also as Goliath tigerfish or Mbenga, lives in Africa in the waters of the Congo River basin and of the Tanganyka Lake. Of great size, on average it measures about 1,5 m of length and 50 kg of weight, the Giant tigerfish is a predator that characterizes for having long teeth, more than 2,5, hence the common name.

About 3 cm long, also the Marbled hatchetfish (Carnegiella strigata) is a Characiformes often present within the domestic walls.

About 3 cm long, also the Marbled hatchetfish (Carnegiella strigata) is a Characiformes often present within the domestic walls © Giuseppe Mazza

Dorado or Dourado are the names with which are commonly indicated the few species of  Salminus (Agassiz, 1829), fishes of size on average of 120-140 cm of length. The genus is native to the large rivers of South America where it appears divided into approximately four species, including Salminus brasiliensis (G.Cuvier, 1816) a Characiformes very popular among the sport fishermen.

The Giant wolf fish or Anjumara (Hoplias aimara Valenciennes, 1847), known also as Traíra and Manjuma, is a fish larger than 1 metre, common in the rivers of the South America.

The Red-bellied piranha or, more simply, the Red piranha (Pygocentrus nattereri Kner, 1858), native to rivers and lakes of South America, is a popular aquarium fish.

The Carnegiella (Carnegiella strigata Eigenmann, 1909) is a small fish, usually 3 cm long native to the basin of the Amazon River in South America. It is a Characiformes known also as Marbled hatchetfish due to the particular shape of its body, laterally compressed and with the ventral part markedly curved whilst the back is almost horizontal.

Order Cypriniformes

The well known Goldfish (Carassius auratus), declined for the aquarists in all forms, is inserted in the immense order of the Cypriniformes that counts almost 5.000 species.

The well known Goldfish (Carassius auratus), declined for the aquarists in all forms, is inserted in the immense order of the Cypriniformes that counts almost 5.000 species © Giuseppe Mazza

They form a very heterogeneous order in which a large variety of fishes comes, almost 5000 species, commonly known as Carps, Gobies, Barbs, Gobiids, Loaches and others more. This number is increasing due to the continuous description of new taxa. Considering the complexity of the order and the difference of opinion about its systematics, here we limit ourselves to consider briefly the main families to which the scholars attribute the status of suborder.

The Cyprinidae, as already said by some scholars raised to the rank of suborder, form a big grouping of fresh water  Actinopterygii where are included about 3000 species, among which Carps and Barbs.

The Cyprinidae) are fishes who in particular characterize for the absence of stomach (agastric) and for having the jaws without teeth. Instead, they are equipped with strong pharyngeal teeth and a masticatory plate formed by a process of the skull with which they are able to crush the hard shells of the mollusks they mainly feed on. The pharyngeal teeth is different depending on the species and is utilized for the taxonomic indentification.

Most Cyprinidae have a pair of barbels.

The Cyprinidae family counts it alone 3.000 species, usually with a pair of barbels. Here a young Common carp (Cyprinus carpio) that may reach the 27 kg.

The Cyprinidae family counts it alone 3.000 species, usually with a pair of barbels. Here a young Common carp (Cyprinus carpio) that may reach the 27 kg © Giuseppe Mazza

The dimensions vary from the about 10 mm of Paedocypris progenetica (Kottelat, Britz, Tan & Witte, 2006) to the 3 m of the Giant barb (Catlocarpio siamensis Boulenger, 1898).

Native to North America, Africa and Eurasia, the Cyprinidae are found in the freshwaters of a good part  of the temperate and tropical lands and are absent in the northernmost areas.

Numerous species of Cyprinidae are commonly indicated with the generic name of Carp where the most known is the Common carpio (Cyprinus carpio Linnaeus, 1758), known also with the names of Eurasian carp or European carp.

The Carp is a freshwater fish native to Europe and Asia and widely introduced in a good part of the world. Behavioural and biological characteristic of this fish is the capacity of being able to cross with other species of the family, in particular with the Goldfish (Carassius auratus  Linnaeus, 1758), originating several varieties, called Carps koi, that distinguish for the colours combination, decoration and quality of the scales.

The Barbel (Barbus barbus), naturally diffused in central-eastern Europe, has been introduced in a large part of the continent.

The Barbel (Barbus barbus), naturally diffused in central-eastern Europe, has been introduced in a large part of the continent © Giuseppe Mazza

Other quite known Cyprinidae are the species of the genus Barbus (Cuvier & Cloquet, 1816), commonly called Barbs due to the presence of two couples of barbels on the snout and for the lower lip having a rear prominence, called median lobe.

Of this genus are to be mentioned the Common barbel (Barbus barbus Linnaeus, 1758), diffused naturally in eastern Europe, in central Europe and introduced in a good part of the continent, the Etruscan barbel (Barbus tyberinus  Bonaparte, 1839), known also as Tiber barbel, and the Padanian barbel or Italian barbel (Barbus plebejus Bonaparte, 1839).

The collective name of Gobies is given to the Gobiidae, family of Actinopterygii with a somewhat troubled systematic position. Some scholar consider them the only representatives of a distinct order, that of the Gobiiformes, others include them in the order of the Perciformes, others, in that of the Cypriniformes.

Systematic position apart, the family of the Gobiidae includes species that characterize for the presence of a ventral disk-shaped sucker resulting from the fusion of the pelvic fins.

The Gobiidae, usually characterized by a ventral sucker fo attaching to the rocks, are almost all marine like this splendid Amblygobius phalaena.

The Gobiidae, usually characterized by a ventral sucker fo attaching to the rocks, are almost all marine like this splendid Amblygobius phalaena © Giuseppe Mazza

For the most part, the Gobiidae are small fishes, like the Dwarf pygmy goby or Philippine goby (Pandaka pygmaea  Qui, 1927) and the Midget dwarf goby (Trimmatom nanus Winterbottom & Emery, 1981) that reach the dimensions of just 1 cm of length.

With more than 2000 known species, the Gobiidae are fishes of broad ecological value diffused in marine, coastal and brackish environments, and of freshwater of tropical and temperte areas. Many species have a high ecological value and are found in extreme environments like some of Chlamydogobius (Whitley, 1930) that are found in the water of geothermal springs.

Usually the Gobies are bottom fishes, some species of the genus Glossobius  (Gill, 1859) are found also in submerged grottoes. Among the several species of the family, are to be mentioned the Common goby (Pomatoschistus microps Kroyer, 1838), an about 9 cm long fish native to the fresh and brackish costal waters of central-northern Atlantic, the Round goby (Neogobius melanostomus Pallade, 1814), usually an about 20 cm species that is found in marine and in freshwater environments of central-western Asia, and the Australian Desert goby (Chlamydogobius eremius Zietz. 1896).

Gobiodon okinawae, 3,5 cm long at most, is one of the smallest extant vertebrates, often present as a curiosity in the public aquaria.

Gobiodon okinawae, 3,5 cm long at most, is one of the smallest extant vertebrates, often present as a curiosity in the public aquaria © Giuseppe Mazza

In the waters of the Mediterranean, the estern Atlantic and the Black Sea live the Paganel goby or Rock goby (Gobius paganellus Linnaeus, 1758), and the Black goby (Gobius niger Linnaeus, 1758). Both species, on average about 15 cm long, display a remarkable resistance to the polluted waters.

And finally, is to be mentioned the Padanian goby, also called European freshwater goby (Padogobius bonelli  Bonaparte 1846), species native to the rivers of northern Italy, Switzerland, and north of the Iberian Peninsula. Usually the dimensions do not reach 10 cm, with the females smaller than the males.

The Cobitidae, by some scholars considered the only membres of a distinct suborder, that of the Cobitoidei, are considered a family that, with more than 250 species, is diffused in the freshwaters ot th Eurasian continent and of north-western Africa.

Of varied shape, fusiform or anguilliform (Pangio Blyth, 1860), the Cobitidae are fishes whose dimensions, usually maintaining on about 10 cm, are inclused from little more than 2 cm (Lepidocephalichtys zeppelini  Havird &Tangjiaroen, 2010)  to more than 50 cm (Lepidocephalichtys manipurensis Arunkumar, 2000).

The Black goby (Gobius niger) even 25 cm long, is the biggest in the genus, frequent in the Mediterranean, east Atlantic and Black Sea.

The Black goby (Gobius niger) even 25 cm long, is the biggest in the genus, frequent in the Mediterranean, east Atlantic and Black Sea © Giuseppe Mazza

The Spined loach (Cobitis taenia Linnaeus, 1758), is found in the slow flowing waterways with sandy or muddy bottom of central and eastern Europe, is absent in Italy.

In Europe freshwaters is reported also the Weatherfish (Misgurnus fossilis Linnaeus, 1758).

The Pond loach (Misgurnus anguillicaudatus Cantor, 1842), is a species native to south-eastern Asia and introduced in various parts of Europe.

Exclusive of peninsular Italy freshwaters are reported the Italian spined loach (Cobitis bilineata Canestrini, 1886), known also as Padanian loach, the Volturno spined loach (Cobitis zanandreai Cavicchioli, 1965), and the Italian golden loach (Sabanejewia larvata De Filippi, 1859). They are small fishes that on average measure little less than 10 cm on the females and 6 cm in the males.

Deserves a special mention the Clown loach (Chromobotia macracanthus Bleeker, 1852), native to the river waters of Indonesia that is a very famous species among aquarists due to its garish livery but with a still poorly known biology.

Absent in Italy, the Spined loach (Cobitis taenia) is found in the slow flowing water courses with sandy or muddy bottom of central and eastern Europe.

Absent in Italy, the Spined loach (Cobitis taenia) is found in the slow flowing water courses with sandy or muddy bottom of central and eastern Europe © Giuseppe Mazza

Native to North America freshwaters, are the Catastomidae, fishes Cypriniformes, that gather about 80 freshawter species, mostly about 60 cm long. Commonly known with the name of Suckers, the main characteristic of the Catastonidae is represented by the mouth opening in subterminal position with big and fleshy lips.

The most popular species is by sure the Chinese sailfin sucker (Myxocyprinus asiaticus Bleeker, 1865), known with various common names such as Chinese high-fin banded shark, Chinese banded shark. Other species to be mentioned is the Longnose sucker (Catostomus catostomus Forster, 1773).

In the mountain streams with strong current of south-eastern Asia live the Gyrinocheilidae, family of fishes Cypriniformes where are included species that characterize for the suction cup mouth with which they anchor to a substratum. The Gyrinocheilidae are commonly known with the name of algae eaters due to their diet made of algae as well as of organic waste. The most known species is the Honey sucker or Chinese algae eater (Gyrinocheilus aymonieri Tirant, 1883), fish as an average about 25 cm long, native to the freshwaters of Sout-East Asia.

Order Gonorynchiformes

The order Gonorynchiformes most known species is the Milkfish or Bangos (Chanos chanos) that can exceed 150 cm in length with a 180 cm and 14 kg record.

The order Gonorynchiformes most known species is the Milkfish or Bangos (Chanos chanos) that can exceed 150 cm in length with a 180 cm and 14 kg record © anarid

They are considered an order of Actinopterygii where are included species equipped with a primitive Weberian apparatus based on the first three vertebrae and one or more ribs, with mouths small and toothless.

The order, to which are ascribed a little less than 40 species whose dimensions vary from 1O to 150 cm, is present in the Pacific and Indian oceans and with some is found in freshwaters of tropical Africa.

The most known species of the Gonorynchiformes is surely the Milkfish or Bangus (Chanos chanos Forsskål 1775), is a big fish, it may exceed the length of 150 cm, that characterizes for the silvery white colour of the body, the fins black edged and the tail particularly forked.

The Milkfish lives usually in tropical marine shallow waters, along the continental shelves and in the vicinity of the islands. Often it enters even the estuaries and goes upstream.

Order Gymnotyformes 

The Gymnotiformes group fishes with very long, sail-shaped, tail only propulsion organ that almost reaches the head like in Electrophorus electricus.

The Gymnotiformes group fishes with very long, sail-shaped, tail only propulsion organ that almost reaches the head like in Electrophorus electricus © Giuseppe Mazza

Often indicated with the name of Knifefishes due to the laterally compressed and elongated shape and with very narow tail, the Gimnotyforms form an order of Actinopterygii to which are ascribed freshwater species found in the rivers north to Argentina.

Typically the Gymnotiformes are fishes that characterize for the very big anal fin, sail-shaped, that develops along all the inferior margin of the body almost up to the head and that forms the only propulsion instrument. The Knifefishes do not have dorsal and pelvic fins. Most of the species have organs able to generate low intensity electric fields, used for orientation and food searching. Some species, like the Gymnotus or South American Electric eel (Electrophorus electricus Linnaeus, 1766), can produce powerful high-potential electrical discharges capable to stun or kill the prey and to keep potential predators far away.

The consistency of the taxonomic heritage of the Gymnotiformes is still far to be defined and to the state appears composed by more than 150 species. Some Gymnotiformes are appreciated aquarium fishes, like Egeismannia virescens (Valenciennes, 1847), Apteronotus albifrons (Linnaeus, 1766) and Gymnotus carapo (Linnaeus 1758), commonly known as Banded knifefish.

Order Siluriformes

The Siluriformes, called catfishes for the presence often of 1-5 pairs of barbels, group heterogeneous species. Malapterurus electricus hunts with up to 400 volts discharges.

The Siluriformes, called catfishes for the presence often of 1-5 pairs of barbels, group heterogeneous species. Malapterurus electricus hunts with up to 400 volts discharges © Giuseppe Mazza

Commonly known as Catfishes, the Siluriformes represent an order of Actinopterygii  whose membres owe their common name to the presence of one to five pairs of barbels, that evoke rightly cats’ whiskers, of which a pair longer that implants on the jaw and the others, smaller, on the mandible. However, some species completely lack barbels.

The Siluriformes form a grouping very heterogeneous in the appearance as well as in the habits.

Mostly Catfishes have a body tapered but flattened on the belly, without scales and frequently with skin bony plates. The mouth is almost always provided of numerous small teeth.

Many Siluriformes present the pectoral fins and the dorsal provided of a strong and sharp spiny ray, often serrated, frequently connected to poison glands. The adipose fin is frequently present.

The Wels catfish (Silurus glanis) is a monstrous fish and may exceed the length of 2,50 cm and 130 kg of weight.

The Wels catfish (Silurus glanis) is a monstrous fish and may exceed the length of 2,50 cm and 130 kg of weight © Giuseppe Mazza

Some species are equipped with additional respiratory organs with which they utilize the athmospheric oxygen and are able to survive for prolonged periods out of the water. Some Catfishes (Malapterurus  Lacépède, 1803) have evolved electric organs able to produce high potential electric discharges with a voltage even higher than 350 volts.

Also in the habits the Siluriformes manifest different styles of life. Most Catfishes live in freshwater environments, but a conspicuous number of species is found in marine and brackish waters. Some species are mainly found in the grottoes, like Phreatobius cisternarum (Goeldi, 1905), a small fish, usually 5 cm long, living in shallow phreatic habitats at the mouth of the Amazon River.

The order of the Siluriformes gathers more than one thousand species of which here below we mention the most representative. The European catfish (Silurus glanis Linnaeus 1758), known also as Siluro or Sheatfish, is a big fish and may even exceed the length of 2,50 m per 130 kg of weight.

But also the fragile and transparent Glass catfish (Kryptopterus bicirrhis), 15 cm long at most and with only one pair of barbels, belongs to the group.

But also the fragile and transparent Glass catfish (Kryptopterus bicirrhis), 15 cm long at most and with only one pair of barbels, belongs to the group © Giuseppe Mazza

Excusively freshwater species and native to central-western Europe, the European catfish has been introduced in several European countries, and, more recently, also in the American continent, often causing serious damages to the local ichthyofauna.

In the same family of the Siluridae is included also the Indian Glass catfish (Kryptopterus bicirrhis  Valenciennes, 1840) diffused in calm waters and flooded prairies of south-eastern Asia. This is a small 15 cm long fish known also as Ghost fish or Underworld catfish due to its characteristic of having in nature a totally transparent body.

With the common name of Eeltail catfishes are indicated about fourty species, all grouped in the family Plotosidae,   that differ for the long tail that reminds that of the eels.

The Plotosidae are about 30 cm long fishes native to the coastal waters of western Pacific.

Within Siluriformes stand also marine species like the Striped eel catfish (Plotosus lineatus) of tropical Indo-Pacific. From the Red Sea via Suez Canal, has entered Mediterranean. The first dorsal fin and the pectoral ones are equipped with dangerous poisonous spines and the stings may aver fatal.

Within Siluriformes stand also marine species like the Striped eel catfish (Plotosus lineatus) of tropical Indo-Pacific. From the Red Sea via Suez Canal, has entered Mediterranean. The first dorsal fin and the pectoral ones are equipped with very dangerous poisonous spines and the stings may aver fatal © Sebastiano Guido

Some species of Plotosidae present the first dorsal fin and the pectoral ones equipped with poisonous spines with which they may cause painful wounds.

In particular, the Striped eel catfish (Plotosus lineatus Thunberg, 1787) has stings that can even be fatal. The species, typical of tropical waters of the Pacific and Indian oceans, has recently arrived also in eastern Mediterranean.

Very singular in appearance are the Loricariidae, family to which are ascribed almost one thousand species that mainly populate the freshwater streams turbulent currents and even with real rapids, from the plains up to 3.000 m of altitude. Some Loricariidae live in calm brackish waters, others in underground habitats.

Native to South America, the Loricariidae owe their scientific name to the presence on the upper parts and on the sides of a real protective armour formed by bony plates and robust scales arranged in 3-4 longitudinal rows.

Conversely, the Suckermouth catfish (Hypostomus plecostomus) is a precious friend of aquarists as perfectly cleans up the glasses from the encrusting seaweeds.

Conversely, the Suckermouth catfish (Hypostomus plecostomus) is a precious friend of aquarists as perfectly cleans up the glasses from the encrusting seaweeds © Giuseppe Mazza

But the most striking anatomic feature of the Loricariidae is represented by the sucker-shaped mouth with big and flat lips with which they can stick to the substrate without incurring the risk of being carried away by the current while they are feeding on herbs and debris.

Among the Loricariidae are to be mentioned the Suckermouth catfish or Common pleco (Hypostomus plecostomus Linnaeus, 1758), among the first membres of the family to be hosted in the aquaria, and the Twig catfish (Farlowella acus Kner, 1853). Both species are native to the tropical freshwaters of South America.

At last, we have not to forget the Black bullhead catfish (Ameiurus melas Rafinesque, 1820), species of North American origin, presently introduced in many regions of the world. Of outstanding resistance, the Black bullhead catfish loves the habitats of slow flowing freshwaters, but is able to bear also polluted environments and to survive for some hours out of the water. The Black bullhead catfish is of average size of 30 cm in length, but may even reach and exceed the 50 cm.

Order Osteoglossiformes

With a record length of 4,5 m and 200 kg, Arapaima gigas is the biggest extant freshwater fish. It breathes the atmospheric air with noisy sips in surface.

With a record length of 4,5 m and 200 kg, Arapaima gigas is the biggest extant freshwater fish. It breathes the atmospheric air with noisy sips in surface © Giuseppe Mazza

They form an order of Bony fishes Actinopterygii  where are included species whose main characteristic is that of having ossified or toothed tongue, hence its scientific name.

The Osteoglossiformes vary greatly in size and shape. With just a 2 cm of length, the Dwarf stonebasher

Pollimyrus castelnaui (Boulenger, 1911) is the smallest membre of the order, whilst the Arapaima (J.P. Müller, 1843) are the giants with about 3 m. Some species are able to produce weak electric fields with which they perceive the presence of possible preys. Some Osteoglossiformes of the families Mormyridae and Gymnarchidae,  stand among the very few vertebrates where the spermatozoon has no flagellum. With more than 250 species, the order of the Osteoglossiformes is diffused in the freshwaters of South America, Australia, southern Asia and Africa.

The African knifefish (Gymnarchus niloticus Cuvier, 1829) known also as Aba, is the only known species of the family Gymnarchidae. Diffused in Africa where is found in the Basin of the Nile and of other rivers, Gymnarchus niloticus is a fish with long and slender body, without caudal and pelvic fins and with a very elongated dorsal fin.

Even 165 cm long, the African knifefish or Aba (Gymnarchus niloticus) is frequent in the NIle basin. Without caudal and pelvic fins has a showy dorsal fin.

Even 165 cm long, the African knifefish or Aba (Gymnarchus niloticus) is frequent in the NIle basin. Without caudal and pelvic fins has a showy dorsal fin © J.C. Harf, eigene Aufnahme

The dimensions usually reach 1,5 cm of length and little less than 20 kg of weight.

With the common name of Freshwater elephant fishes or Elephant fishes are known the Mormyridae, family of Osteoglossiformes native to Africa. With more than 200 specie, the common name of the Elephant fishes refers to the presence of particularly protruding fleshy outgrowths on the mouth.

The Mormyridae are weakly electric fishes, very heterogeneous in dimensions and shape, the smallest ones are only 5 cm long, whilst the biggest reach up to 1,5 m. Various species of Mormyridae can adapt to live in aquarium.

The Dwarf elephant fish or Dwarf stonebasher (Pollimyrus castelnaui Boulenger, 1911) is a Mormyridae of small size, only 2 cm long, living in habitat of landlocked freshwater of central-western southern Africa.

Arapaima (J.P. Müller, 1843) is a genus of Osteoglossiformes whose specific composition is not yet clearly defined whose membres stand among the biggest freshwater fishes in the word, with a length of even 3 metres.

The Elephantnose fish (Gnathonemus petersi) reaches 35 cm. The unusual tunk has tactile and gustatory terminations. The tail emits an electric field used as radar.

The Elephantnose fish (Gnathonemus petersi) reaches 35 cm. The unusual tunk has tactile and gustatory terminations. The tail emits an electric field used as radar © Giuseppe Mazza

Locally known also with the names of Pirarucu or Paiche, that means red fish, the Arapaima are native to the basins of the Amazon and of the Essequibo rivers, in South America.

Among the distinctive characters of the genus is surely to be mentioned the structure of the swim bladder particularly developed and formed by a tissue that, like a lung, allows to use the atmospheric oxygen.

The Nile Arowana or African bonytongue (Heterotis niloticus G. Cuvier, 1829) is an up to 100 cm long fish with a weight of about 10 kg that in its look reminds much the Arapaima. Native to the central Africa hydrographic basins, the species has been introduced in various other African basins.

Of great nutritional importance for the locals, the African Arawana is the subject of highly successful aquaculture practices due to the ease of feeding and the good tolerance for overcrowding.

Order Batrachoidiformes

As the name states, Sanopus splendidus is the most elegant Batrachoidiformes, the so-called toadfishes, mainly presenti in the tropics but also in temperate waters.

As the name states, Sanopus splendidus is the most elegant Batrachoidiformes, the so-called toadfishes, mainly presenti in the tropics but also in temperate waters © Allison & Carlos Estape

They form an order of Actinopterygii to which belong very unusual shaped species that resembles that of an amphibian, hence the scientific name of Batrachoidiformes, and also the common one of Toadfishes or Frogfishes.

The look of the Batrachoidiformes is unmistakable, with the broad and flattened head and the back of the body compressed laterally. The eyes, rather big, are in dorsal position and are located very far forward like in Sanopus splendidus.

The mouth is ample and equipped with robust and pointed teeth. Under the jaw are present dermal protuberances or barbels that recall those of the scorpion fishes. In some of them are present other skin appendages around the nostrils. Each branchial operculum is equipped with spines and the scales may be absent or are very small. There may also be present two lateral lines and some species are provided with bioluminescent organs (photophores).

The first dorsal fin is very short and equipped with rigid spiny rays, conversely, the second is long and supported by soft rays. The pectoral fins are big and the caudal is rounded. Another quite unique characteristic  of the Toadfishes is their capacity of emitting sounds by utilizing the swim bladder.

Halobatrachus didactylus, present but rare in Mediterranean, may reach 50 cm. They are benthic fishes, with wide and flat head camouflaged by barbels. They feed on small fishes, gastropods and polychaetas worms. They live isolated and not migratory but gather in the reproductive time emitting loud sounds with the swim bladder.

Halobatrachus didactylus, present but rare in Mediterranean, may reach 50 cm. They are benthic fishes, with wide and flat head camouflaged by barbels. They feed on small fishes, gastropods and polychaetas worms. They live isolated and not migratory but gather in reproductive time emitting loud sounds with the swim bladder © Ana Santos

Small and medium-sized fishes, with maximum lengths around the 60 cm, usually the Batrachoidiformes have a uniformly livery of a colour varying from brown to greenish. However, there are species with bright colours like the Coral toadfish or Cozumel Gorgeous toadfish (Sanopus gorgeousus Collette et alii, 1974) of the Caribbean Sea coral reefs.

With almost one hundred species, the  Batrachoidiformes are diffused in all tropical seas and, more fragmentarily, also in the temperate ones. They are particularly common in the American waters. Benthic and predatory fishes, the Toadfishes are usually found in coastal waters on hard and also muddy bottoms and are present also in the coral reefs.

Some species are euryhaline and live also in brackish waters. Some Toadfishes live permamently in freshwaters. In the Mediterranean waters is present but rare the Lusianian toadfish (Halobatrachus didactylus Bloch & Schneider, 1801), fish that can be even 50 cm long. The Mediterranean toadfish is recognizable due to the presence of 4 dark saddle-shaped dorsal spots on a livery of colour variable from reddish brown to green to yellow.

Order Gadiformes

Even 2 m long, the Atlantic cod (Gadus morhua) is the biggest of the Gadiformes, mainly marine fishes with advanced pelvic fins, at the pectorals level © Joachim S. Müller.

Even 2 m long, the Atlantic cod (Gadus morhua) is the biggest of the Gadiformes, mainly marine fishes with advanced pelvic fins, at the pectorals level © Joachim S. Müller

Called also Anacanthini due to the absence of spines, the Gadiformes form an order whose membres characterize in particular for the singular and varied structure of the fins.

In fact, unlike the more evolved forms where the caudal fin is neatly distinct, the most primitive forms have the dorsal fin, the caudal and the anal, united each other to form a continuous structure like in the Anguilliformes.

Within the order, the Bregmacerotidae distinguish mainly for the presence of a long spiny ray of the first dorsal fin protruding on the head like a sort of horn.

The ventral fins are often equipped with very long filamentous rays and typically the pelvic fins, when present, are located in front or below the pectoral fins. The tail is short and biforked.

About 1 m long, the Pacific cod (Gadus macrocephalus) lives in schools in the cold northern waters between 100 and 400 m of depth, but can go down even up to 1280 m.

About 1 m long, the Pacific cod (Gadus macrocephalus) lives in schools in the cold northern waters between 100 and 400 m of depth, but can go down even up to 1280 m.© Gregory C Jensen

The Gadiformes are physoclist fishes, that is with the swim bladder not communicating with the digestive system.

The Gadiformes include numerous species mainly spread in the marine waters of the cold or temperate regions. In the Mediterranean the Gadiformes are present with few species, some of them fractionated in subspecies.

Mostly of broad ecological value, they are diffused in various environments, membres of the order are found in various environments, from the coastal one to the abyssal. Some species live also in brackish waters of the estuaries some is permanently freshwater.

The tropical species are typically deep-sea.

Only the Freshwater cod or Burbot (Lota lota Linnaeus, 1758) is considered with certainty a freshwater fish.

Also Blue whiting (Micromesistius poutassou) can reach 1000 m. Frequent in the Atlantic and the Mediterranean, distinguishes for the small mouth and the big eyes.

Also Blue whiting (Micromesistius poutassou) can reach 1000 m. Frequent in the Atlantic and the Mediterranean, distinguishes for the small mouth and the big eyes © Vsevolod Rudyi

Many species of Gadiformes are edible and of great commercial value for the world economy.

Considering the high number of species of Gadiformes, here below we provide brief information notes about the species most representative of the order and we refer to the specific sheets for any further information. Several species belonging to different genera, in particular to Gadus, are indicated with the collective name of Cod.

The Atlantic cod (Gadus morhua Linnaeus, 1758), commonly known also as White cod or Northern cod and commercially known also white the name of “codling”, is without any doubt one of the most important fishes for the human nutrition worldwide. The Cod is conserved dried (stockfish), or salted and seasoned (salted cod).

Other species of the genus are the Greenland cod (Gadus ogac Richardson, 1836) and the Pacific cod (Gadus macrocephalus Tilesio, 1810.

The Poor cod (Trisopterus minutus) is a modestly sized fish, less than 25 cm, present in north-east Atlantic.

The Poor cod (Trisopterus minutus) is a modestly sized fish, less than 25 cm, present in north-east Atlantic © Sylvain Le Bris

The Silvery pout (Gadiculus argenteus Guichenot, 1850) a small sea fish, usually not exceeding the 9 cm in length. It characterizes for having very big head and eyes and the oblique mouth and for the presence of 3 small dorsal fins. The livery is of grey-pinkish colour on the dorsal parts, silvery on the sides and the belly. The Silvery pout lives in deep waters, usually under 200 m.

The Whiting (Merlangius merlangus Linnaeus, 1758) is a fish that reaches the length of 50 cm. It has a protruding snout with small mouth, and three contiguous dorsal fins of which the central one is more developed. The livery of the Whiting is of brown colour on the back, whitish on the belly.

Diffused in the Atlantic, it is present also in the Black Sea and in the Adriatic. It usually lives on mobile bottoms where it feeds on small fishes and of crustaceans like the Grey shrimp (Crangon crangon Linnaeus, 1758) for whose rarefaction it is considered responsible.

Amply diffused in the Atlantic and common also in the Mediterranean waters is the Blue whiting Micromesistius poutassou Risso, 1827).

Analogous is the range of the European pollock or Pollack (Pollachius pollachius) that may reach 130 cm and may go further north up to Iceland.

Analogous is the range of the European pollock or Pollack (Pollachius pollachius) that may reach 130 cm and may go further north up to Iceland © trece grados

Known also with the name of Poutassou, the Blue whiting is a Gadiformes that usually measures about 25 cm and distinguishes for the small mouth and the big eyes. Pelagic fish, the Blue whiting lives in open waters at depths between 100 and 1000 m.

The Poor cod (Trisopterus minutus Linnaeus, 2758), known also as Busbana, distinguishes for the presence of a small barbel under the mouth and of two anal fins separated from each other. The Poor cod is a fish of modest size, less than 25 cm, with body of uniformly brown yellowish colour dorsally, silvery on the sides and white ventrally.

The species is found in the Atlantic waters and in the western Mediterranean ones. Usually it forms schools living on muddy seabeds at various depths.

The Pouting or Bib (Trisopterus luscus Linnaeus, 1758) is a species of the northern Atlantic whose presence in the Mediterranean is to be confirmed. The species is known also with the names of French pout or Brown cod.

The Common mora (Mora moro) is an about 50 cm abyssal Gadiformes found on sandy bottoms, usually beyond 1000 m. On the jaw is present a short barbel.

The Common mora (Mora moro) is an about 50 cm abyssal Gadiformes found on sandy bottoms, usually beyond 1000 m. On the jaw is present a short barbel © jgrimshawl

The European hake or Common hake (Merluccius merluccius Linnaeus, 1758) is a fish that distinguishes for the widely incised and straight mouth, armed with strong protruding teeth and with the mandible longer than the jaw. The body of the European hake is slender and may even reach the length of 140 cm and a weight of 15 kg. The livery takes on dark shades on the back, silvery on the sides. The European hake lives in the eastern Atlantic waters and in those of the Mediterranean and the Black Sea where is found on muddy or sandy seabeds also at depths of less than 400 m.

The Greenfish or Pollack (Pollachius pollachius Linnaeus, 1758) is a Gadiformes living in the north-eastern Atlantic waters, at depths less than 100 m.

Very similar in appearance to the Saithe or Coalfish (Pollachius virens Linnaeus, 1758) with whom it shares part of its own range, the Saithe can be even more than 120 cm long and presents a livery bronze in colour uniform on the dorsal parts and whitish on the ventral ones. The snout is pointed, with widely protruding jaw.

Usually 40-50 cm long, Forkbeard (Phycis phycis) is a Gadiformes present in Mediterranean and eastern Atlantic coasts from France and Spain to Macaronesia.

Usually 40-50 cm long, Forkbeard (Phycis phycis) is a Gadiformes present in Mediterranean and eastern Atlantic coasts from France and Spain to Macaronesia © Bernat Espigulé

The Haddock (Melanogrammus aeglefinus Linnaeus,1758), is a fish having a very similar appearance as the Atlantic cod (Gadus morhua Linnaeus, 1758) from which differs for having a taller body with a solidly built body and eyes decidedly bigger. Under the mouth is present a small barbel. The dorsal fins are three and the anal fin is wide.

The livery is of a colour varying from silvery to greenish on the back, with a characteristic round black spot at the height of the pectoral fins. Usually it is smaller than the Cod and may reach the length of one metre.

The Haddock has a range covering the northern Atlantic where it lives in the cool waters with sandy or pebbly bottoms. It feeds on marine invertebrates and small fishes.

The Common mora or Good-eyed cod (Mora moro Risso, 1810), is a Gadiformes that differs for the very big eyes and the silvery colour.

The Aiglefin (Melanogrammus aeglefinus), known also as Haddock, is a fish similar to Cod but with higher body and decidedly bigger eyes.

The Aiglefin (Melanogrammus aeglefinus), known also as Haddock, is a fish similar to Cod but with higher body and decidedly bigger eyes © Biopix

It has an elongated body, as an average 50 cm long, that tapers towards in the caudal peduncle. On the mandible is present a short barbel. The dorsal fins are two, the fore being higher than the rear one and of triangular shape. The livery is of brownish colour with silvery reflections on the back and on the sides, darker on the belly.

It is an abyssal fish found on sandy seabeds of deep waters, usually deep more than 1000 m. The Common mora is spread in a vast range that includes the north-eastern Atlantic, the western Mediterranean and the temperate regions of the Pacific and Indian oceans.

The Forkbeard (Phycis phycis Linnaeus,1766) is a Gadiformes of medium size, usually of 40-50 cm long.

Similar in the look to many other membres of the order, the Forkbeard distinguishes for having the large mouth with big lips. The livery is uniformly dark, brown or grey.

The Burbot (Lota lota) diffused in freshwaters of the arctic zones and in the great pre alpine lakes of northern Europe, Italy included, is the only freshwater Gadiformes.

The Burbot (Lota lota) diffused in freshwaters of the arctic zones and in the great pre alpine lakes of northern Europe, Italy included, is the only freshwater Gadiformes © lindra

The Forkbeard is diffused in the waters of the north-eastern Atlantic on sandy or pebbly seabeds up to about 60 m of depth.

The Burbot (Lota lota Linnaeus, 1758) is the only species of the order surely with freshwater habits. It is a fish with very elongated body, on average about 100 cm long, at times even 180 cm per a weight exceeding the 30 kg. The mouth is very large with one barberl of the jaw. Typically the dorsal fins are two, of which the fore one is short and the rear very elongated.

The livery has a marbled colouration varying from brown to green to yellow on the back, whitish on the belly.

The Burbot is vastly diffused in the freshwaters of the arctic regions and is present in the big pre-alpine lakes of northern Europe, Italy included.

Order Lophiiformes

Even 2 m long, the Angler (Lophius piscatorius) present in eastern Atlantic, Mediterranean and in the Black Sea, is the biggest extant Lophiiformes.

Even 2 m long, the Angler (Lophius piscatorius) present in eastern Atlantic, Mediterranean and in the Black Sea, is the biggest extant Lophiiformes © Pietro Formis

They represent an order of  Actinopterygii fishes whose membres characterize for the presence of a fleshy appendage or mobile antenna present on the front, the so-called illicium. This is a bioluminescent structure serving to attract the preys which they feed on. The head is big, adorned withy bony crests and spines with a wide mouth armed with several sharp teeth. The body of the Lophiiformes has no scales. Another characteristic of many Lophiiformes is their capacity to extend the jaw and the stomach, particularly elastic, allowing to swallow preys up to twice their size. The Lophiiformes are also known for their marked sexual dimorphism withe the males that are significantly smaller than the female. A further particularity of several species of these singular fishes is the phenomenon of sexual parasitism. During the reproduction, the male adheres to the female and, while transferring its own sperm to the female, draws its nourishment from the body of the partner.

The Lophiiformes  are found at a depth of 1000 m and even more. Presently, in this order are known about 350 species, grouped in about 18 families of some of which we give here below some essential information.

Family  Antennariidae – Frogfishes

The Antennarius use their pelvic fins like legs for moving, at times with leaps, on seabeds like this Antennarius multiocellatus, hence, perhaps, the name of frogfishes© Allison & Carlos Estape

The Antennarius use their pelvic fins like legs for moving, at times with leaps, on seabeds like this Antennarius multiocellatus, hence, perhaps, the name of frogfishes© Allison & Carlos Estape

Commonly called Frogfishes, they form a family to which are ascribed marine species that distinguish for presenting a stocky body with big spherical and laterally compressed with the mouth turned upwards and equipped with 2-4 more or less irregular rows of small bristly teeth on the upper and lower jaw.

On the head are present three spines of which the front one is free and mobile, modified as bait (illicium).

The eyes are small and located laterally. The protruding pectoral fins are utilized for moving among the corals and on the rocks.

The gill opening, shaped like a tube, is employed as jet propulsion organ.

Benthic animals, up to about 300 m of depth, they have a livery blending with the environment whose colour varies from red to orange to yellow.

They have a fishing line with bait, the illicium, they move up and down when they see a fish to attract its attention and swallow it whole when it gets closer curiously.

They have a fishing line with bait, the illicium, they move up and down when they see a fish to attract its attention and swallow it whole when it gets closer curiously © Giuseppe Mazza

Usually the females of some species lay several thousands of eggs immersed in a floating gelatinous mass; in other species, instead, the females carry the eggs stuck to their body.

With about 50 species, the Antennariidae are diffused in all tropical and subtropical seas but the Mediterranean. They live preferably in waters deep up to 300 metres, on coral and rocky seabeds.

Here we are mentioning the most known species of the family.

The Commerson’s frogfish or Giant frogfish (Antennarius commerson Lacépède, 1798), is a euryhaline fish that may reach the length of 45 cm. It is found in the Indian and eastern Pacific waters.

The Commerson’s frogfish, like other frogfishes, lays eggs that are encapsulated in a floating mucous mass, called “egg raft”.

Like this Antennarius striatus, they are fishes with a huge mouth and dilatable stomach that allows to swallow preys as large as twice their size.

Like this Antennarius striatus, they are fishes with a huge mouth and dilatable stomach that allows to swallow preys as large as twice their size © Sebastiano Guido

The Longlure frogfish (Antennarius multiocellatus Valenciennes, 1837), known also Flagpole frogfish, distinguishes for having the body covered by scales modified in dermal spicules that give him a spiny look that somewhat remind the warts on a toad.

The livery is quite variable, however always used for camouflaging. The background colour can vary from red to yellow, to dark green, to brown, with scattered black spots and with several ocellar drawings, hence the specific name, that imitate the osculi of the sponges with which this fish blends. In some situations the Longlure frogfish may get an almost completely colouration. The Longlure frogfish lives in the western Atlantic waters.

The Striated frogfish or Hairy frogfish (Antennarius striatus Shaw, 1794), is an Antennariidae that may reach teh size of about 25 cm of length. It distinguishes for having the body covered with forked and thin spines that look like hairs, hence the common name of Hairy frogfish.

What's more, they are extremely mimetic, like this Black angler (Antennarius commerson) that may assume any colour and shape, here we would think to a sponge.

What’s more, they are extremely mimetic, like this Black angler (Antennarius commerson) that may assume any colour and shape, here we would think to the a sponge © Keoki Stender

Conversely, the specific name comes from the presence of some subparallel streaks that start behind each eye.

The Striated frogfish is found in eastern Atlantic in an environment associated with the coral reefs.

Another congeneric species is the Painted frogfish (Antennarius pictus Shaw, 1794), Antennariidae fish known also as Black angler or Spotted frogfish.

Usually little less than 30 cm long, it is a species of the Indo-Pacific waters that characterizes for having the body partly covered by few outgrowths similar to small warts and several ocellar designs that simulate the oscula of the sponges with which this fish blends. The Painted frogfish lives among the coral reefs of the waters of the Pacific and Indian oceans.

Family Lophiidae – Goosefishes

Lophius budegassa, at most 1 m long, is a species similar to the Anglerfish who shares its range.

Lophius budegassa, at most 1 m long, is a species similar to the Anglerfish who shares its range © Luis Pérez Berrocal

They represent a family of Lophiiformes whose components are known as Anglers or Goosefishes.

The family unites 30 known species and is diffused in all temperate, subtropical and tropical seas excepting the Antarctic. By sure the most known species of the family and of the order is the Anglerfish (Lophius piscatorius Linnaeus, 1758). Called also Monk, the Anglerfish characterizes for the big mouth turned upwards, with the lower protruding jaw from the upper one and equipped with a fringe of cutaceous appendages. The mouth has several sharp teeth. The livery is basically brown-greenish on the dorsal parts, white on the ventral. The fins are edged dark. The dimensions usually reach the length of 90 cm in the female, with a 2 m record, and little more than a half in the male.

The Anglerfish is found in the North Sea waters, in the eastern Atlantic ones, in the Mediterranean and in the Black Sea where usually prefers the sandy and stony seabeds between 20 and 1000 metres of depth. Anoher species is the Lophius budegassa (Spinola 1807), fish quite similar to the Anglerfish with whom it shares the range.

Family Ogcocephalidae – batfishes

As the name suggests, the batfishes definitely are not beautiful. This Ogcocephalus nasutus, with 4 legs and one horn evokes more a rhino than a fish.

As the name suggests, the batfishes definitely are not beautiful. This Ogcocephalus nasutus, with 4 legs and one horn evokes more a rhino than a fish © Mickey Charteris

Often known as Batfishes or Seabats due to their unusual look reminding that of the Rays, the Ogcocephalidae are a family of Lophiiformes whose membres are for the most part adapted to benthic habits, haence also the common name of Deep-sea batfishes. However, it must be kept in mind the some species are found in shallow  coastal waters and also in estuaries.

The Shortnose batfish (Ogcocephalus nasutus Cuvier, 1829), is a deep sea species found in western Atlantic and in the Caribbean where it loves the sandy or muddy bottoms with debris or with prairies of marine phanerogams.

It is a fish may be little less than 40 cm long whose generic name refers to the shape almost hooked of the head, whilst the specific name alludes to the pointed rostrum on the snout.

The head is flattened and the remainder of the body is depressed and has a triangular shape.

The Spotted batfish (Ogcocephalus radiatus) by sure is not more attractive. Its illicium is so short that the preys have almost to reach its mouth.

The Spotted batfish (Ogcocephalus radiatus) by sure is not more attractive. Its illicium is so short that the preys have almost to reach its mouth © Giuseppe Mazza

The livery is of colour varying from blackish to grey, to reddish in the doral parts, at times adorned with dark and clear spots. The Sorthnose batfish females lay eggs from which develop swimming larvae that deposit on the bottom and transffom in the juvenile shapes.

Another species of the family and of the genus is the Polka-dot batfish (Ogcocephalus radiatus Mitchell, 1818), a little less than 38 cm long fish, native to the Atlantic coast.

Similar in the look to a Ray, the Polka-dot batfish has broad and depressed body, arrow-shaped.

Of benthic habits, that prefers the seabeds where it preys crustaceans, mollusks and also young fishes it attracts also with the help of a substance contained in the rostrum.

Order Ophidiiformes

The Ophidiiformes include species with elongated body, almost anguilliform. Their head is usually small and the body is covered by smooth or completely absent scales. The Fierasfer or Pearl fish (Carapus acus), particularly thin and long less than 10 cm that lives as a parasite in the digestive tract of the Echinoderms.

The Ophidiiformes include species with elongated body that are almost anguilliform. Their head is usually small and the body is covered by smooth or completely absent scales. The Fierasfer or Pearl fish (Carapus acus), particularly thin and long less than 10 cm that lives as a parasite in digestive tract of the Echinoderms © Xavier Rufray

Included for a long time with the status of suborder among the Perciformes, presently the Ophidiiformes are considered as a distinct order of Actinopterygii to which are ascribed species typically presenting the elongated body, almost anguilliform. Fishes Ophidiiformes, most of them have small head and body covered by smooth of completely absent scales. The dorsal fins are long and usually the anal fin very long and continues with the caudal. The ventral fins, missing in several species, are implanted much anteriorly and often resemble barbels.

The dimensions of the Ophidiiformes are very varied, included from the 5 cm of the Bighead brotula Grammonus opisthodon, Smith 1934) to the about 2 m of the Scaleline cusk (Lamprogrammus shcherbachevi Cohen & Rohr, 1933). The Ophidiiformes are widely diffused in environments of tropical and subtropical marine waters, often in deep waters. Some species colonize the underground waters of the caves, others are found in freshwaters. In the Mediterranean waters are reported the Allen’s brotula (Cataetyx alleni Byrne, 1906), fish of abyssal habits, just over 10 cm long, the Pearl fish or Fierasfer or Sea urchin (Carapus acus Brünnich, 1768), very thin in shape, no more than 10 cm, that lives as a parasite in the digestive tract of Echinoderms, and the Yellow brotula (Benthocometes robustus (Goode and Bean, 1886) reaches a maximum length of 15 cm.

With 20-25 cm of length, the Parophidion vassali, present in the Mediterranean and nearby Atlantic, is in comparison a giant

With 20-25 cm of length, the Parophidion vassali, present in the Mediterranean and nearby Atlantic, is in comparison a giant © Sylvain Le Bris

Moreover, other Ophidiiformes living in the Mediterranean waters are the Snake blenny (Ophidion barbatum  Linnaeus, 1758) and the Red cockerel (Parophidion vassali Risso, 1810), fishes measuring both about 25 cm.

Order Percopsiformes

Native to the North American freshwaters, the Percopsiformes are considered an order of Fishes Actinopterygii whose scientific name refers to the resemblance of its membres with the most known Perca (Linnaeus, 1758). Well represented starting from the Upper Cretaceous (about 70-66 million years ago), nowadays the order is almost completely extinct and of it survive only about ten species.

Usually, the Percopsiformes are fishes of small size, included between the 5 and the 20 cm of length, depending on the species, and of various appearance that somewhat reminds the Perch of the order of the Perciformes. Diffused mainly in freshwater environments of North America, they are present with few species with W-boreal distribution. The Pirate perch (Aphredoderus sayanus Gilliams, 1824) is a Percopsiformes frequent in the eastern coastal waters of USA, well-known predator of mosquito larvae.

The Percopsifomres, frequent in the Cretaceous, count now only a ten species. Aphredoderus sayanus is a predator of mosquito larvae that lives in USA.

The Percopsifomres, frequent in the Cretaceous, count now only a ten species. Aphredoderus sayanus is a predator of mosquito larvae that lives in USA © Michaeln Zambardino

The Southern cavefish (Typhlichthys subterraneus Girard, 1859) is an exclusive species of the karst caves of eastern United States.

The Alabama cavefish (Speoplatyrhinus poulsoni Cooper & Kuehne, 1974) has been discovered in underground pools of the Key Cave National Wildlife Refuge in Alabama.

To the order of the Percopsiformes belongs also the Swampfish or Ricefish (Chologaster cornuta Agassir, 1853), a few, about 4 centimetres species, diffused in the freshwaters of the United States Atlantic coastal plain.

Order Polymixiiformes

They represent an order of Fishes Actinopterygii to which belong only about ten species included in the only genus Polymixia. They are small in size, ranging from just over 15 cm up to around 45 cm, with big eyes and mouth, a couple of long barbels and small fins.

The Southern cavefish (Typhlichthys subterraneus) is another survivor, present in the karst caves of eastern USA

The Southern cavefish (Typhlichthys subterraneus) is another survivor, present in the karst caves of eastern USA © Eric C. Maxwell

The Polymixiiformes, diffused in all oceans and in the Red Sea, are known for having the body covered with abundant mucus, hence the scientific name. The Pacific beardfish (Polymixia berndti Gilbert, 1905) stands amongst the most known of the membres of the order. It is a fish that can be even more than 45 cm long found in the Pacific and Indian oceans.

Order Esociformes

Order of Fishes Actinopterygii, the Esociformes unite morphologically and ecologically species very varied that characterize mainly for presenting the dorsal fin and the anal one rather far back and for the absence of adipose fin. Also the dimensions of the Esociformes  are very different and vary from the about 8 cm of the European mudminnow to the about 140 cm of the Northern pike.

The order gathers about 12 species, all of freshwaters environments, most of them, known with the name of Pike, are attributed to Esox, genus diffused in rivers and lakes of North America and of Europe. In Europe several species of Esociformes are reported, of which the most known is the Northern pike.

And also the small Swampfish (Chologaster cornuta), present in the freshwaters of the USA Atlantic coastal plain, is a Percopsiformes.

And also the small Swampfish (Chologaster cornuta), present in the freshwaters of the USA Atlantic coastal plain, is a Percopsiformes © Daniel Folds

The Northern pike (Esox lucius Linnaeus, 1758) is an Esociformes that characterizes for the large flattened and elongated head like a duck’s beak, from where also the name of Luccio Papera as indicated by the locals. The large mouth is armed with a huge number, several hundred, of robust and hooked teeth placed also on the tongue. The Northern pike can measure even 1,40 m of length and weigh more than 20 kg. The livery is varied, more frequently of greenish brown colour with dark spots on the dorsal parts, yellowish white on the ventral ones.

Widely diffused in North Amerca and in some regions of Eurasia, the Northern pike has been subject to repeated introductions for the sport fishing with consequent hybridizations and often impairment of the local ichthyofauna. In North America lives the Muskellunge or Muskie (Esox masquinongy, Mitchil, 1824), the biggest among the predatory fishes of the Mississippi River. The pikes play an important rôle in maintaining the balance of the ecosystems, because they feed preferentially on preys dead or weak or sick, as well as they limit also the excessive proliferation of other fishes, particularly Cyprinidae.

Other European species of the genus are the Cisalpine pike or Southern pike or Italian pike (Esox cisalpinus Bianco & Delmastro, 2011),  species endemic to northern Italy where prefers habitats of stagnant waters or with weak currents, and the Aquitanian pike (Esox aquitanicus  Denys et alii, 2014), native to the hydrographic basins of the Charente and of Adour in south-west France.

The Esociformes group freshwater fishes, like the Pike (Exos lucius), that have the dorsal and the anal fins placed in a rear position.

The Esociformes group freshwater fishes, like the Pike (Exos lucius), that have the dorsal and the anal fins placed in a rear position © Giuseppe Mazza

Another species of the order is the Mudminnow (Umbra krameri  Walbaum, 1792), is a small fish just over 15 cm log. Native to the waters of the Danubian basin, during the last century the Mudminnow has been introduced in various regions of Europe.

Order Osmeriformes

For a long time included among the Salmoniformes, the Osmeriformes are considered an order of Fishes

Actinopterygii, the Osmeriformes unite species of very varied look and biology and usually they are provided of an adipose fin. Amply diffused in the two hemispheres, excluding the temperate and warm zones, membres of the

Osmeriformes can be found in marine environments, brackish and freshwater. Some live also in  depth environments. The coastal species usually migrate in the rivers for the reproduction ( anadromous).

The Smelt (Osmerus eperlanus Linnaeus, 1758) is a small fish on average 20 cm long, diffused in the European coastal waters of the Atlantic Ocean.

In North America lives the Muskellunge (Esox masquinongy) the biggest among Mississippi predator fishes. The pikes have an important rôle in maintaining the balances of the ecosystems, because they usually feed o weak or ill preys, as well as because they also limit the excessive proliferation of fishes like the Cyprinidae.

In North America lives the Muskellunge (Esox masquinongy) the biggest among Mississippi predator fishes. The pikes have an important rôle in maintaining the balances of the ecosystems, because they usually feed o weak or ill preys, as well as because they also limit the excessive proliferation of fishes like the Cyprinidae – Engbretson, Eric U.S. Fish and Wildlife Service

The Chinese icefish (Neosalanx tangkahkeii Wu, 1931) is a just 6 cm long species living in the tropical or subtropical brackish waters of China.

Other species of Osmeriformes is Opisthoproctus soleatus (Vaillant, 1888), fish diffused in the Pacific, Indian and Atlantic oceans where normally lives at depths between 500 and 700 m. Usually the dimensions maintain on the length of 10 cm.

Order Salmoniformes 

Important order of Fishes Actinopterygii, the Salmoniformes that unite several species, marine and freshwater, that often characterize for the presence of two dorsal fins where the second is adipose.

Commonly known with the names of Salmons, Trouts, Whitefishes, Lennok and other more, the Salmoniformes are fishes with the body usually elongated and fusiform, of quite various size, averagely included from just over 10 cm to more than 1 m of length.

The Grayling (Thymallus thymallus) belongs to Salmoniformes, order rich in marine and freshwater species, characterized often by an adipose second dorsal fin.

The Grayling (Thymallus thymallus) belongs to the Salmoniformes, order rich in marine and freshwater species, characterized often by an adipose second dorsal fin © Thomas Menut

Also the appearance is very varied, with the mouth that in many species, like Salmons and Trouts, is very ample and richly provided with large teeth placed also on the tongue, whilst in others, like the Grayling (Thymallus thymallus  Linnaeus, 1758), is small and with very small teeth.

The dorsal fins are two, of which the rear is adipose. The caudal fin, usually ample, may present the edge forked or truncated.

In the Salmoniformes the ventral fins are planted far back, at times behind the first dorsal fin. Usually the caudal fin can be forked with truncated margin.

In most Salmoniformes the livery characterizes for the presence of small spots and dots of black and red colour with metallic reflections. The Whitefishes have the body uniformly silvery.

The genus Coregonus counts more than 70 species mainly in the cold waters of the boreal hemisphere. Coregonus lavaretus, known as Lavaret or Powan, is highly sought after due to the high quality of its flesh. In the late 1900s has been introduced in Italy where now is diffused in the northern and central lakes of the peninsula.

The genus Coregonus counts more than 70 species mainly in the cold waters of the boreal hemisphere. Coregonus lavaretus, known as Lavaret or Powan, is highly sought after due to the high quality of its flesh. In the late 1900s has been introduced in Italy where now is diffused in the northern and central lakes © Thomas Menut

The Salmoniformes are mostly found in the seas, the rivers and the lakes of the boreal hemisphere, in the temperate and cold regions up to the polar ones. They have been abundantly introduced in zones with suitable environmental characteristics. They are carnivorous fishes, some like the salmons prey on other fishes, others, like the  Grayling feed on insects, others more are planktonofagous.

The Salmoniformes usually are stenothermal fishes, that prefer the cold and well oxygenated waters. Many species are anadromous and during the reproductive period they leave the sea where they usually live and, guided by the sun and by their extraordinarily acute sense of smell, they go up the rivers to get back in the freshwaters where they were born. Reached the site of reproduction, the salmons fast, while the maturation of eggs and sperm is completed. After mating, the females lay on gravelly bottoms at shallow depths a not very high number of eggs. In several species, many of the reproducers pass away once the ovideposition is done.

The order of the Salmoniformes  includes more than 200 species grouped in various genera of which in this text we furnish essential information referring to the relevant taxonomic sheets for further information.

The Trout is present in Europe with various races with unsure taxonomy. The Sea trout goes uprivers to reproduce.

The Trout is present in Europe with various races with unsure taxonomy. The Sea trout goes uprivers to reproduce © Janne Passi

Whitefishes is the name with which are commonly indicated the more than 70 species of Coregonus (Linnaeus, 1758), genus diffused mainly in freshwaters ot the cold regions of the boreal hemisphere.

Some Whitefishes of the northernmost zones live in marine waters ans are anadromous.

In the freshwaters of central and northern Europe is found the Lavaret or European whitefish (Coregonus lavaretus Linnaeus, 1758). Particularly sought after due to the high quality of the fleshes, the Lavaret, called also Freshwaters bass, at the end of 1900 has been introduced in Italy where now is diffused in the northern and central lakes of the peninsula.

To the same genus is attributed the Maraena whitefish (Coregonus maraena Bloch, 1779), species also known with the name of Lake herring, often mistaken with the Lavaret.

The name of Trout is the name that unites several species of Salmonidae and in particular those belonging to the genera SalmoOncorhynchus and Salvelinus.

The Steelhead trout (Oncorhynchus mykiss Walbaum, 1792), called also Rainbow trout, is a species native to the waters of North America and from there introduced in good part of Europe.

With the collective names of Salmons and Trouts are commonly indicated the species of Salmo, genus whose range includes Europe, North Africa and Anatolia including several regions of central-western Asia.

Among the most known of the genus stands the Atlantic salmon (Salmo salar Linnaeus, 1758),  anadromous species indicated simply with the name of Salmon. Diffused along the coasts of North America, the Atlantic salmon is present as result of the human activity in almost all continents, Australia included. Finally, the name of Mediterranean trout or Peninsular trout, it includes under the specific name of Salmo ghigiia (Pomini, 1941) all the Trouts native to the Italian peninsula.

A distinct specific validity is attributed to the Sicilian trout or Sicilian macrostigma trout (Salmo cettii, Rafinesque, 1810) to the Carpione del Garda (Salmo carpio  Linnaeus, 1758), exclusive to the Garda Lake and to the Fibreno carpione or Fibreno trout (Salmo fibreni Zerunian – Gandolfi, 1990), fish endemic to the Natural Reserve of the Lake Posta Fibreno. The Adriatic trout or Illyrian trout (Salmo obtusirostris Heckel, 1851), commonly known also as Adriatic salmon or Soft mouth trout, is typical of the karst streams of the northeast of the Adriatic Sea.

Salmo trutta fario is a variety living in particularly mountain rivers and streams. In waters rich in carotenoids, its flesh takes on a pinkish colour like those of the Salmon, hence the term, of no taxonomic value, of Salmon trout. An analogous effect is obtained with appropriate food in aquaculture.

Salmo trutta fario is a variety living in particularly mountain rivers and streams. In waters rich in carotenoids, its flesh takes on a pinkish colour like those of the Salmon, hence the term, of no taxonomic value, of Salmon trout. An analogous effect can be obtained with appropriate food in the aquacultures © Giuseppe Mazza

The Trout (Salmo trutta Linaneus, 1758) is present, with various races whose texonomy is still unclear, in all Europe, as well as in northern Africa, Anatolia and Central Asia. The dimensions and the livery of the Trout vary quite significantly depending on the environment where it lives.

The marine and lake specimens, respectively called Sea trout and Lake trout, may exceed the length of 1 m and present the silvery body with small X-shaped dark spots like the Salmons.

The Brown trout is a variety living in rivers and streams, especially mountainous. Usually it does not exceed the length of 50 cm and has a livery enlivened by characteristic round spots, black on the back and bright red or brown on the sides, arranged in way to form a horizontal series. The pectoral and ventral fins are of yellowish colour. In waters particularly rich in carotenoids, the meats of the Trout get a pinkish colour like those of the Salmon, hence the term, of no taxonomic value, of Salmon trout.

The Rainbow trout (Oncorhynchus mykiss), also called Steelhead, is a species native to North America waters and from there introduced in good part of Europe.

Rainbow trout (Oncorhynchus mykiss), also called Steelhead, is a species native to North America waters and from there introduced in good part of Europe © Bruce Deagle

Abant trout (Salmo abanticus Tortonese, 1954), is a freshwater Salmoniformes whose dimensions maintain under the 50 cm of length. Initially considered as a race of Salmo trutta, later on a distinct species, presently the Abant trout has an indefinite status and is cited as a strain limited to the lake of abant, in Anatolia. Garda carpione (Salmo carpio Linnaeus, 1578), is a Salmoniform typical to the Garda Lake in whose waters completes its entire life cycle.

The Marble trout (Salmo marmoratus Kottelat & Freyhof, 2007), once considered a subspecies of Salmo trutta, more recently considered as a species in itself. The Mable trout is known for the subalpine Adriatic fluvial basins, from the streams even at high altitude, to the lake basins and to the plain watercourses.

The Sicilian trout or Sicilian macrostigma trout (Salmo cettii  Rafinesque, 1810) characterizes for the presence of black punctiform spots and the absence of red spots. The Sicilian macrostigma trout is known for some watercourses of south-eastern Sicily.

Native to North America, Brook trout (Salvelinus fontinalis) has been introduced in Europe at the end of 1800, with sometimes harmful results for the local ichthyofauna.

Native to North America, Brook trout (Salvelinus fontinalis) has been introduced in Europe at the end of 1800, with sometimes harmful results for the local ichthyofauna © Giuseppe Mazza

Chars is the name with which are indicated the species of  Salvelinus (J. Richardson, 1836), genus of Salmoniformes native to North America where is found in fresh, cold and transparent waters. Various species have developed anadromous habits. The Chars are fishes having very varied dimensions, included from the 15 cm of

Salvelinus lonsdalii (Regan, 1809), diffused in freshwaters of England, to the 150 cm of the Lake char or American Lake trout (Salvelinus namaycush, Walbaum, 1792), native to the freshwaters of the northern regions of North America.

The Brook char or Brook trout (Salvelinus fontinalis Mitchill, 1814), is a Salmoniform with very colourful livery with fins edged with white tha usually has dimensions less than 40 cm. Native to the cold and temperate waters of North America, the Brook char has been introduced in Europe at the end of the nineteenth century, often with harmful results for the local fish fauna.

The Adriatic grayling or Bluefin grayling (Thymallus aeliani Valenciennes, 1848) is freshwater fish endemic to the river Po basin and to other waterways of northern Italy.

Adriatic or Bluefin grayling (Thymallus aeliani) is a freshwater fish endemic to the river Po basin and to other water courses of north Italy.

Adriatic or Bluefin grayling (Thymallus aeliani) is a freshwater fish endemic to the river Po basin and to other water courses of north Italy © lifegraymarble

The European grayling or Redfin grayling (Thymallus thymallus Linnaeus, 1758), originally present in the central-northern Europe, has been introduced in various European regions, Italy inncluded. The Lenok

(Brachymystax lenok Pallas, 1773) is a Salmoniformes, about 70 cm long, that is found in the freshwaters of northern Asia, from Siberia to Korea. It s a fish that may reach even 1 metre of length and a weight of 15 kg. Hucho 

Günther, 1866 is a genus of Asian origin whose membres stand among the most massive freshwater fishes.

To the genus are ascribed 4 species of which the most known is surely the Danube salmon (Hucho hucho Linnaeus, 1758), fish that may reach large dimensions, up to 150 cm of length, and a weight of about 50 kg. Once exclusive to the Danube River and its tributaries, the Danube salmon has been introduced in other European and North African rivers. Another species of the genus is the Siberian salmon or Taimen (Hucho taimen   Pallas, 1773), by some believed to be a subspecies of the Danube salmon and nowadays relegated in eastern Asia.

Order Myctophiformes

Benthosema pterotum belongs to the Myctophiformes, an order grouping small-sized species, averagely 10 cm long, with laterally compressed body, big mouth and eyes and often, when living in deep water, with luminescent organs to attract the preys, hence the name of lanternfishes and lampfishes.

Benthosema pterotum belongs to the Myctophiformes, an order grouping small-sized species vastly diffused in all seas. Thes are averagely 10 cm long, with laterally compressed body, big mouth and eyes and often, when living in deep water, with luminescent organs to attract the preys, hence the name of lanternfishes and lampfishes © uwkwaj

Yore merged to the Aulopiformes, the Myctophiformes are considered a distinct order of Actinopterygii that unites small species, averagely of 10 cm, with body compressed laterally, mouth and eyes usually big. In the rear part of the body, anterior to the caudal fin, is present a flap of skin tissue devoid of rays, called, adipose fin.

In relation to depth and predatory habits, usually in these fishes are present  light-emitting organs (photophores). In reference to this characteristic, many species and in particular the Myctophidae, are often indicated with the collective name of Lanternfishes. In addition to that of the bioluminescence, another important characteristic of the lanternfishes is represented by unusual reproductive modalities, defined as sexual parasitism.

Common to other abyssal fishes like Lophiiformes, the sexual parasitism consists in the fact that for reproducing the male clings to the body of the female and shares with her its own circulatory system. In this way, the male can feed itself and in the meantime ensure to the female a flow of sperm sufficient for the fecundation of the eggs.

Analogous is the look of the Atlantic flashlightfish (Kryptophanaron alfredi) who however belongs to the Trachichthyiformes order.

Analogous is the look of the Atlantic flashlightfish (Kryptophanaron alfredi) who however belongs to the Trachichthyiformes order © Allison & Carlos Estape

The Myctophiformes are vastly diffused in all seas, from the warm equatorial to the warm polar ones, where they can be found in deep waters and far from the coasts. For the great majority they are bathypelagic fishes and represent an important part of the marine food chains. In the Mediterranean Sea waters are common numerous species of Lanternfishes, several of which beach in huge quantities in the Messina strait.

Among the Lanternfishes reported also for the waters of the Mediterranean, we mention the Spothead lantern fish

(Diaphus  metopoclampus Cocco, 1829), an about 7 cm long fish, the Skinnycheek lanternfish or Opaline lanternfish (Benthosema pterotum  Alcock, 1890), of same length, and the Benoit’s lanternfish (Hygophum benoiti  Cocco, 1838), on average about 8 cm long. Other species of the order are the Neoscopelidi, known also as Blackchins, deep sea fishes, diffused in a localized manner in the tropical and subtropical seas of the wole world, but the Mediterranean. To other order, that of the Trachichthyiformes, belongs the Atlantic flashlightfish (Kryptophanaron alfredi Silvester et Fowler, 1926), an about 12 cm long fish, of central-western Atlantic who owes its name to the presence of a typical bioluminescent structure close to the mouth.

Order Ateleopodiformes

The Ateleopodiformes are deep sea fishes, absent in the Mediterranean, populating also the bathyal zone. in north-western Pacific lives Guentherus katoi almost 70 cm long – National Oceanic and Atmospheric Administration, no known copyright restrictions –

The Ateleopodiformes are deep sea fishes, absent in the Mediterranean, populating also the bathyal zone. in north-western Pacific lives Guentherus katoi almost 70 cm long – National Oceanic and Atmospheric Administration, no known copyright restrictions –

They are an order of Actinopterygii to which are ascrived species usually large in size, at times even 2 m long. Known with the common name of Jellynose fishes, the Ateleopodiformes are fishes with swollen snout and with very elongated body, characterized by a very long anal fin and a tiny caudal one.

The dorsal fin is short and high, whilst the ventral fins are usually reduced to only two rays placed in the front position.

Fishes of abyssal habits that populate also the bathyal zone, the Ateleopodiformes live in the waters of the Indian, Pacific and eastern Atlantic oceans where is found the Loppe’s tadpole fish (Ijimaia loppei Roule, 1922), among the biggest species of the order with a length that may reach even the 2 m. In north-western Pacific is reported the species Guentherus katoi (Kuwayama et Hiorate, 2008), deep sea fish that measures just under 70 cm. This order is not present in the Mediterranean Sea.

Order Stomiiformes

The Pacific viperfish (Chauliodus macouni) so called due its long teeth, is a Stomiiformes long almost 30 cm that can go down up to 4390 m of depth.

The Pacific viperfish (Chauliodus macouni) so called due its long teeth, is a Stomiiformes long almost 30 cm that can go down up to 4390 m of depth © Jackson W.F. Chu

The Stomiiformes are an order to which are attributed species of a very varied look, of small size that usually reach few dozen centimetres.

The smallest membre of this order is the Dwarf round mouth (Cyclothone pygmaea Jespersen & Tåning, 1926), species native to the Mediterranean that reaches just the length of 1,5 cm. The biggest of the Stomiiformes, is the Obese dragonfish (Opostomias micripnus Günther, 1878), species amply diffused in the Pacific, Indian and Atlantic oceans that is about 50 cm long.

In relation to the abyssal habits, these fishes are abundantly equipped with light-emitting organs (photophores) arranged in two parallel rows on the ventral part of the body.

Many species have big mouths armed with long sharp teeth that extend beyond the eyes, like the Stoplight loosejaw (Malacosteus niger Ayres, 1848) of the central-eastern Atlantic whose jaw can be widely extroverted for catching small crustaceans and fishes it feeds on.

Characterized by the red bioluminescence, unique ability in fishes, and by a big orbital photophore, the Dragonfish (Malacosteus australis), locally known as Southern stoplight loosejaw is a Stomiiformes present in the subtropical and temperate waters of the austral hemisphere.

Characterized by the red bioluminescence, unique ability in fishes, and by a big orbital photophore, the Dragonfish (Malacosteus australis), locally known as Southern stoplight loosejaw is a membre of Stomiiformes present in the subtropical and temperate waters of the austral hemisphere © ESRI, Dr. Beinart, Tracey T. Sutton

Some Stomiiformes characterize for having the mouth practically vertical without or with small teeth.

Several species have upward-facing telescopic eyes and most Stomiiformes present under the mouth a barbel, sometimes very long, often equipped with photophores that attract the preys.

The body of these fishes, covered by thin scales that come off easily or has no scales, has usually a dark colouration, black or brown, which camouflages them with the dark environment of the ocean depths where they live.

Among the most typical deep sea fishes, even if not infrequently they can be found in surface waters, membres of the Stomiiformes are met in all the seas, polar ones included.

Among the species of the order we report here below the mentioned species.

The Ribbon sawtail fish (Idiacanthus fasciola) is a dragonfish with barbels of north Atlantic. It's almost 50 cm long and has great jaws with long teeth.

The Ribbon sawtail fish (Idiacanthus fasciola) is a dragonfish with barbels of north Atlantic. It’s almost 50 cm long and has great jaws with long teeth © Ken Graham

The Pacific viperfish (Chauliodus macouni Bean, 1890) is a Stomiiformes long just under 30 cm  of the deep Pacific waters that distinguishes for the long teeth, hence its own common name.

The Ribbon sawtail fish (Idiacanthus fasciola Peters, 1877) belongs to the group of the so-called Barbeled dragonfishes, fishes that characterize for having the very big jaws rich in long teeth. It is a fish which usually does not reach the 50 cm in length. Of mesopelagic habits, it is found in the deep waters of northern Atlantic.

Characterized by the red bioluminescence, unique capacity among fishes, and by a big orbital photophore, the

(Malacosteus australis Kenaley, 2007) is a Dragonfish with barbels whose body dimensions uaually maintain under the 20 cm. Called by the locals Southern stoplight loose jaw, this species is known for the subtropical and temperate waters of the austral hemisphere.

Subclass DIPNOI

The subclass Dipnoi, old grouping among the vertebrates with jaws (Gnathostomata) includes forms that breathe with gills and lungs.

The subclass Dipnoi, old grouping among the vertebrates with jaws (Gnathostomata) includes forms that breathe with gills and lungs © Vincent Rufray

They form one of the oldest groupings among all the jawed vertebrates (Gnathostomata). They include forms that characterize for the double breathing capacity, trough gills and through lungs, hence the name of Dipnoi or Dipneusti and also of Lungfishes.

The lung of these fishes originates from a ventral diverticle of the pharynx and during its development lengthens  and twists around the pharynx itself and takes on a dorsal position.

To the double breathing capacity of the Dipnoi corresponds the separation between the general, branchial, and pulmonary blood circulation.

Nowadays, with the progress of knowledge in the fishing field, we know that this condition is rather older than the Dipnoi themselves and is amply practically shared by archaic forms of all clades of Osteichthyes.

They are therefore called lungfishes, like these Neoceratodus forsteri living in the freshwaters of eastern Australia.

They are therefore called lungfishes, like these Neoceratodus forsteri living in the freshwaters of eastern Australia © Jan Stefka

It seems that also the Placodermi,  paleozoic fossil fishes presently considered all extinct, were equipped with gas bladders corresponding to those of the most primitive Bony fishes and, consequently, to the lungs of the terrestrial vertebrates.

Of very ancient origins, fossil remains testify to their presence already in the Devonian (about 400 million years ago), the Dipnoi form a grouping  that still keeps very archaic characters like the spine column without vertebral bodies, and the tail that, primitively heterocercal in the fossil species, becomes diphycercal in the modern forms.

The fins remained unchanged from the Paleozoic to nowadays and still maintain the primitive structure with double series of rays (biseriate archipterygium).

In this regard, it must be remembered that in the past for the double breathing capacity and for the archipterygian fin, considered the ancestor of the limbs of all Tetrapods, Amphibians, Reptiles, Birds and Mammals, the theory prevailed that the Dipnoi were the connecting link between Fishes and Amphibians.

When the streams in which they live do dry up, the Protopterus, like this Protopterus dolloi, wrap themselves in a muddy cocoon and breathe air waiting for the rains.

When the streams in which they live do dry up, the Protopterus, like this Protopterus dolloi, wrap themselves in a muddy cocoon and breathe air waiting for the rains © Giuseppe Mazza

Later on and for a long time, prevailed the theory according which the liaison rôle between fauna. and the waters and the terrestrial on has been done by the Crossopterygii, in the specific by the Rhipidistia as equipped with even appendages more similar to limbs than to fins. Very common in the Paleozoic, the Rhipidists probably became extinct already in the Permian, by the end of the Paleozoic (about 250 million years ago).

Presently, recent molecular biology research have brought back in fashion the theory after which the true ancestors of the Tetrapods are the Dipnoi  and not the Ripidisti. The present forms of the Dipnoi have elongated body, at times anguilliform, covered by thin cycloid scales arranged in a tile-like formation.

The head is wide and flattened, with rather small lateral eyes. The mouth opens ventrally at the extremity of the snoutand is provided with sucecssive rows of teeth arranged in a fan shape, characteristic this that does not find any matches in any other species of vertebrates.

The presence of choanae, placed behind the upper lip and open-ended in the oral cavity, has made these fishes deserve the appellation of Choanoichthyes. The branchial openings are coverd by an operculum.

This Australian Neoceratodus forsteri, swimming on the surface, clearly takes the air with its mouth.

This Australian Neoceratodus forsteri, swimming on the surface, clearly takes the air with its mouth © Gavin Goodyear

Important distinctive character is represented by the dorsal fin that, variously developed, is whole and continues with the diphycercal tail and the anal, also undivided; only one caudal fin is present. The pectoral and ventral fins are flattened and covered by tiny scales. In some species they are particularly fleshy and are supported by bony elements and allow these fishes to proceed by walking on the bottom.

In the Dipnoi the lateral line is clearly defined, whilst there is no blowhole. Another character of structural primitivity of the Dipnoi is the presence of a spiral valve in the intestine that remains short and straight.

The sexes are separated and the reproduction of the Dipnoi  occurs uniquely in aquatic environment. After coupling, the females lay the first eggs, of 2 or 3 millimetres of diametre, covered by jelly.After 3-4 weeks small larviform-looking babies are born provided with outer gills that recall those of the Brachiopterygii and of the Urodelan Amphibians.

It should be noted that the current species of Dipnoi populating the waters of the Australian continent are able to breathe air only for a limited period of time, whilst the African and the South American ones are able to overcome long drought periods  (even four years), taking refuge in a den dug in the mud of the seabed and sealed with protective mucus.

This Protopterus aethiopicus breathes in the grass out of the water. For years it was therefore thought that the Dipnoi were the ancestors of the Tetrapoda, the first terrestrial vertebrates.

This Protopterus aethiopicus breathes in grass out of water. For years it was therefore thought that Dipnoi were the ancestors of Tetrapoda, the first terrestrial vertebrates © Jason

Inside the den, these fishes survive entering a sort of inactivity (aestivation) during which they breathe directly the atmospheric air and significantly reduce their metabolic activities.

During the aestivation they just use up their own fat reserves, whilst the metabolism waste products are converted into urea, instead of ammonia.

Very common in the Triassic (about 250-200 million years ago), era in which they probably did populate the freshwaters of all Pangaea, supercontinent where were cncentrated all the lands emerged during the Paleozoic and the beginning of the Mesozoic, the Dipnoi  have subsequently suffered a rapid decline during the Permian.

Nowadays, almost completely extinct, the Dipnoi  are represented only by 6 species of which we mention the

Lepidosiren paradoxa (Fitzinger, 1837), unique of the genus and typical of the freshwaters of the swamps of the Amazon rainforests, the  Neoceratodus forsteri (Frefft, 1870), endemic to rivers of north-eastern Australia and the Marbled lungfish (Protopterus aethiopicus Heckel, 1851), reported for the inner waters of Africa.

Suclass CROSSOPTERYGII

Then, looking at the fossils of Latimeria, fish inserted in the subclass Crossopterygii they thought that they were the fishes who colonized the mainland

Then, looking at the fossils of Latimeria, fish inserted in the subclass Crossopterygii they thought that they were the fishes who colonized the mainland © R.d207bea75a0adeb620180d0085980e43

Considered among the most archaic within all jawed vertebrates (Gnathostomata), the Crossopterygii form a subclass of Bony fishes whose fossil remains testify their presence since the Devonian beginning (more than 400 million years ago). Almost completely extinct at the end of the Mesozoic, in the same era when disappeared the dinosaurs (about 65 million years ago), now the Crossopterygii are represented only by the Coelacanth (Latimeria (Smith, 1939)), discovered in 1938 by Marjorie E. D. Courtenay-Latimer, curator biologist of the National History Museum of East London, South Africa.

True extant fossils, the only two species of Latimeria maintain numerous characteristics of primitiveness, like the homologous dermatocranial vault with the bony plates of Placoderms and with the cranial bones of Palaeoniscoids and with the cranial bones of old Amphibians.

Moreover, the primitiveness of the Crossopterygii is documented by the texture of the scales of cosmoid type that cover the body. The cosmoid scale represents the oldest form that has evolved from the bone plates of the first fishes  (Ostracoderms and Placoderms) now extinct.

Other characteristics of primitiveness of these fishes are noted in the spine where the single vertebrae lack the body and in the teeth that characterize for being covered by enamel not distributed evenly like in the Labyrinthodont  Tetrapods.

With the discovery, still extant, of the Latimeria chalumnae here shown and of the analogous Latimeria menadoensis this hypothesis became almost a certainty.

With the discovery, still extant, of the Latimeria chalumnae here shown and of the analogous Latimeria menadoensis this hypothesis became almost a certainty

Also the tail still maintains a diphycercal primitive stucture and is divided into three lobes, the median one including the continuation of the dorsal chord (notochord).

The name of the subclass refers to the structure of the fins that is always of Archipterygium type but, unlike the Dipnoi where it is biserial, is tipically the monoserial one, that is with only one series of lateral rays that are implanted in the median axis.

Are an exception the Coelacanthiformes where the fins, though of Archipterygium type, have no rays. Typically, in these fishes the pectoral and anal fins, of a fleshy consistency and supported by bony elements, are utilized also for moving on the seabed. The swim bladder, uneven and dorsal, is strongly reduced and is not working as hydrostatic organ and not even as accessory respiratory organ.

It is believed that the Fishes Crossopterygii, whose origin is found in an early detached branch of the Dipnoi,  already in the Paleozoic are split into two divergent phyletic lines, Actinistian and Rhipidists. To the grouping of the Actinistian, all marine and characterized by a fin without rays and not referable to the monoserial model of the Crossopterygii, is ascribed only one order, that of the Coelacanthiformes, now represented only by the Coelacanth (Latimeria Smith, 1939), to which belong two species.

Also because the scales of Latimeria chalumnae seem those of fossil coelacanth and remains of Tetrapoda, not to talk of the structure of the skull and of the vertebrae.

Also because the scales of Latimeria chalumnae seem those of fossil coelacanth and remains of Tetrapoda, not to talk of the structure of the skull and of the vertebrae © Cordenos Thierry

The West Indian Ocean Coelacanth (Latimeria chalumnae Smith, 1939), is a big fish, up to 2 m of total length per an average weight of 80 kg. It characterizes for the colouration of the body typically bright blue.

Its range is fragmented and is found in the waters of the Mozambique Channel and of the Comoros Islands at depths between 200 and 600 metres.

The Indonesian Coelacanth (Latimeria menadoensis Pouyaud et al., 1999) found in Indonesia in the waters of Sulawesi (former Celebes), is distinguishable from the Comoros Coelacanth for the brown colouration of the body and through a biomolecular investigation of the DNA.

The Coelacanths, whose biology is poorly known, are viviparous animals and the females produce big eggs rich in yolk (telolecithic) of almost 10 cm of diametre. Upon birth, the babies measure more then 30 cm in length.

In the group of the RipidistiCrossopterygii presently all extinct, are included fossil forms, attributed to various orders, (Osteolepiforms, Porolepiforms, Stomiiforms).

But now the molecular biology has replaced the hypothesis and this Protopterus annectens seems to smile because it was the Dipnoi who originated the terrestrial vertebrates. In reality the winner is the life, and all extant beings are winners, on equal terms, because through the millennia they have found the way to reach us alive.

But now with molecular biology has replaced the hypothesis and this Protopterus annectens seems to smile because it was the Dipnoi who originated terrestrial vertebrates © Giuseppe Mazza

Unlike the Coelacanthiformes, the forms included in the grouping of the Rhipidists did populate the continental waters. Unlike the Dipnoi, the present Crossopterygii of the order of the Coelacanthiformes live exclusively in marine waters where they usually stand at 300-400 m of depth.

To conclude this brief overview, it should be remembered that rightly the Crossopterygii Rhipidist Osteolepiformes are considered the ancestors of the terrestrial vertebrates. This hypothesis gets its foundations in the evaluation of the skull structure and of the vertebrae, as well as of the teeth that are of labyrinthodont type and of the Archipterygium fins that prelude to the legs of the Tetrapods.

This hypothesis has superseded the previous belief that the ancestors of the terrestrial Vertebrates (Amphibians, Reptiles, Birds, Mammals) should instead be found in the Dipnoi.

Nowadays, recent molecular biology research have brought back into vogue the theory after which it’s the Dipnoi  and not the Crossopterygii of the group of the Rhipidists to have originated the terrestrial Vertebrates.

In reality the winner is the life, and all extant beings are winners, on equal terms, because through the millennia they found their way to arrive alive to the present day.

In reality the winner is the life, and all extant beings are winners, on equal terms, because through the millennia they found their way to arrive alive to the present day © Laurent Ballesta