Family : Syngnathidae
Text © DrSc Giuliano Russini – Biologist Zoologist
English translation by Mario Beltramini
This quite strange marine animal, around which many legends were born, since the ancient times, when they thought that some gigantic versions of it did exist, as terrestrial monsters and as marine, although the biologists had given it a name to the genus as Hippocampus, that is “horse monster”, is a bony fish com- mon in all the warm and temperate seas.
The members of this genus, which, after some zoological biologists, are afferent to the order of the Gasterosteiforms (Gasterosteiformes), the same to which belongs, for instance, the stickleback, the needlefish, and other 150 species, whilst, after others, the order to which it belongs is that of the Syngnathiforms (Syngnathiformes); the ICZN has not yet expressed a final judgement), but which, independently from the denomination of the order, converge into the family of the Syngnathids (Sygnathidae), are wonderful fishes, extremely fragile (as the Great Barrier Reef), essential for the marine biologic-ecologic balance (exploited for this reason, also as one of the biologic indicators, of the health status of the seas), where, for many of the numerous species composing the genus, they are getting increasing problems due to the low density of population.
This is indicative of an increasing pollution of the sea waters which host them; the life of these wonderful bony fishes is always more complicated, The reproduction in the wild is decreasing continuously and, together with it, the density of population up to critical values for some species, so that they have become part of the red list of endangered species of the IUCN. An example is the ever rarer Dwarf seahorse (Hippocampus zosterae). We shall treat here the Hippocampus guttulatus Cuvier, 1829, which, with the analogous Hippocampus hippocampus, is much abundant in the Mediterranean.
But numerous are the species forming the genus Hippocampus, among which the already mentioned Dwarf seahorse (Hippocampus zosterae), found in the tropical waters, the Hippocampus hudsonius, also at home in the warm tropical waters, characterized by an attractive livery, with bright colours, or the Hippocampus kuda, with bright yellow livery, or the Hippocampus barbouri, also with yellow livery, but with a less bright shade, mixed with the white. They are all species which will be treated in specific texts. However, as it may have noticed, they are animals with coloured liveries (more or less intensely and in a variegated way), with often associated appendices, in some cases of particular shape, so much to camouflage the fish with a marine plant, as it happens for some species of seahorse. In the specific, the Hippocampus guttulatus, has, as we shall see, a red purple-violaceous livery, with associated some needle-like expansions, in particular on the head and part of the back.
These animals have always held an old relationship with the human beings, not only in mythological and of legend terms, but, for instance, at commercial level, as they are traded (the CITES already rules strictly their trade, but now, for some tropical species in danger of extinction, forbids severely their fishing an trading), as ornamental fishes, utilized in the aquariology, or, in the past, once caught, they were placed to dry up, and then utilized for making necklaces or bracelets. Although if nowadays such practice, which falls within the so-called Industrial Zoology, is strongly banned, the contraband is unluckily always around the corner.Zoogeography
The Hippocampus guttulatus is autochthonous to the coastal waters of the Mediterranean Sea, the Tyrrhenian Sea, but is found also along the Adriatic coasts, the Ionian Sea, the Sea of Sicily; about fifteen years ago they have started sampling and fishing also whole groups in the English Channel, sedentary in those waters.
The outer look of the Hippocampus guttulatus and, generally, also for the other members of the family of the Sygnathidae, is quite strange and does not recalls at all the outer and macroscopic morphology of a bony fish, which is the case of this animal. As a matter of fact, it has special characteristics, shared with other seahorses, which differentiate them from all the other fishes. The head as an elongated shape and recalls that of a horse. The muzzle, thin and tubular, ends in a very small mouth; this is a characteristic, as well as the big eyes if compared to the size of the head, of all the members of the family of the Sygnathidae. The eyes are lateral and much developed for guaranteeing a good vision and are independent each other; this means that they may be moved each one in a direction. This increases the field of vision.
This adaptation, from the evolutionary point of view has generated in these fishes, which are not capable to swim very well, allowing them to see preys and predators well in time.The gills are small. The ventral fins are missing (from this the poor swimming capacity, which makes them seem, when moving, as they were floating), whilst the only dorsal fin is placed in a median position and endowed of great mobility, with probably a function of propulsive type. As briefly said before, all the members of the genus Hippocampus do not swim too well, and the type of movement and swimming which characterizes them is very specific, so much to have them immediately recognized.
The Hippocampus guttulatus, like all other Hippocampus, swims keeping in vertical position, by means of the pectoral fins placed on the sides of the body. This posture has affected also the conformation of the skeleton, especially on the neck. In fact, the corner formed by the head with the rest of the body, is almost a right angle, whilst the other bony, cartilaginous and agnate fishes have a spinal column which continues, horizontally, with the head.The body of the various members of the genus Hippocampus is covered by a real cuirass and the Hippocampus guttuluatus is not an exception. This in the specific, and generally, is formed by rings, evidenced by white sripes, idependently from the colour of the livery, and plates. The rings in the Hippocampus guttulatus (in the other species they differ a little in number) are about fifty and go from the head to the tail. Some plates (the white part) connect to them. Both rings and plates are of bony origin.Moreover, in the Hippocampus guttulatus body (as in the other species in a more or less marked way) grows in diameter, from the tail, rounded for a certain number of turns inwards or towards the belly, with voluntary mobility, often extended acting as a rudder and as holding point), to the head, which is quite disproportioned, due to its big size, if compared with the entire axis of the body.
Needle shaped bony structures are present on all the head, the initial part of the trunk and part of the sides, with variable length. Also, but this characteristic is common also to the other species, some longitudinal crests, equipped with tubercles, are present. Also the tail is crossed by four small crests, two dorsal and two ventral. This particular skeleton which, we remind is of violaceous-purple red colour in the Hippocampus guttulatus, recalls a medieval horse, covered by the heavy armour for tournament or battle.
The tail is common and much particular characteristic of the seahorses: it is prehensile and serves for clinging to rocky ledges or aquatic plants. The caudal fin is absent, while there is a quite small anal fin. The lack of the caudal fin is due to the conformation of the tail, ending in an angled and sharp tip. The gills, as for the other fishes, represent the respiratory system and have a particular structure. They communicate with an internal cavity, of remarkable size, and open outward by means of a narrow opening, which is difficult to be seen. Externally, they appear as a delicate and elegant tuft. Most of the bowels are located in the region of the neck.
The males have, in the anal region, a pouch or “marsupium”, very developed, without bony covering and provided with a muscular sphincter. This pouch is only little outlined in the female of all the species of the genus Hippocampus, and this, biologically speaking, has assigned the role of pregnancy to the father. The Hippocampus guttulatus, both males and females, are 17-18 cm long, as an average.
Usually, the biotope of the Hipocampus guttulatus, as well as that of the Hippocampus hippocampus are the coastal zones and the marine areas where are present plantations of weeds. As they are not good swimmers, they perform only short displacements, leaving themselves to be transported by the marine currents. The particular conformation of the mouth allows them to seize small planktonic animals, which they nourish of.Ethology-Reproductive Biology
Before beginning the description of the biological cycle of the Hippocampus guttulatus, we have to say that, as a principle, this applies also to the other members of the genus Hippocampus, and it is good to do before a more detailed description of the anal pouch of the male, which is in charge pregnant in this genus of bony fishes. This is a pouch formed by two skin folds, placed on the tail outside which the genital pre opens.
The female of the seahorse in general, in the specific of Hippocampus guttulatus, produces the eggs through its ovaries, but then it is the male who incubates them till completion of the gestation.
Before coupling, the male and the female perform a delicate nuptial dance, once this is ended the two fishes copulate. They tie by means of the tails, staying vis-à-vis. Then, the female emits the eggs, which she introduces by means of the “genital papilla”, into the anal marsupium of the male. As soon as entered there, the eggs are fecundated by the sperms of the male. At this point, through a cascade of endocrine signals and bio-chemical factors which stimulate the vascularisation, etc., on the walls of the pouch develops an intricate “capillary network” which renders it very similar to a “gravid uterus”. Around each fecundated egg do take form some independent alveoli which perform gaseous exchanges with the walls of the pouch; this allows the developing embryo to receive O2 and to get rid of the CO2. In the meantime, the female gets away and since this moment ignores the progeny.
After some time, the embryos come out from the egg, but still remain, and for long, inside the anal marsupium. Finally, the male moves to cooler waters (because richer of oxygen than the warms ones) and begins the “delivery”. The sphincter of the anal marsupium starts to relax, while the animal writhes spasmodically. The young get out from the pouch, at times with the head ahead, at times with the tail. As soon as out, they flounder for some seconds, unable to swim, then, once familiar with the environment, they get away by themselves (apt-presocial offspring), swimming vertically. They develop in few months, reaching the adults stage. The vulnerability index of this species is of 24 over 100.
Hippocampus hippocampus microcoronatus Slastenenko 1938; Hippocampus hippocampus microstephanus Slastenenko 1937; Hippocampus longirostris Schinz, 1822; Hippocampus ramulosus Leach, 1814.