Family : Lepisosteidae
Text © Dr. Giuseppe Mazza
English translation by Mario Beltramini
Present in North American slow watercourses, Atractosteus spatula is often defined a living fossil due to its solid armour of ganoid scales and its alligator’s snout © Giuseppe Mazza
Known as Alligator gar due to the shape of the snout, broad and flattened like that of the alligators and armed with several teeth, Atractosteus spatula (Lacépède, 1803) belongs to the order of the Lepisosteiformes and to the family of the Lepisosteidae, the same as Lepisosteus osseus.
The common English name “Alligator gar” is formed by “alligator”, evident reference to the look of the head, and “gar”, an old English name used to indicate these characteristic fishes having long jaws and sharp teeth. The term has nowadays entered the common nomenclature of the North American Lepisosteidae. These fishes are often referred to as living fossils, as their evolutionary line is very old and several anatomical characteristics have remained recognizable over a very long period of time. The first gars have been reported in the fossil record from about 100 million years ago.
The genus Atractosteus, created by Rafinesque in 1820, comes from the Greek “átraktos”, merged, and “ostéon”, bone, with reference to the body covered by the characteristic ganoid scales, very hard and tough. Conversely, the specific term spatula comes from the Latin “spatula”, diminutive of “spatha”, blade wide and flat, reminding the wide and flat shape of the snout.
Can exceed 3 m in length and reach 140 kg in weight, while the anal and dorsal fins located near the tail recall ancestors that existed 100 million years ago © G. Mazza
Zoogeography
Atractosteus spatula is native to northern America. Its natural range includes the Mississippi basin and several watercourses flowing into the Gulf of Mexico, from the basin of Mississippi southwards up to coasts of the Gulf including also part of Mexico. It is present in the great rivers and in their tributaries, but also in the systems of slow waters connected to the main watercourses. Moreover, the species has been introduced outside its natural range, also in some regions of South-East Asia, especially for reasons related to sport fishing.
Habitat-Ecology
The adult Alligator gars live mainly in the slow-flowing or stagnant waters of great rivers, lakes, swamps, bayous and floodplains, where they mainly frequent the quiet areas, the oxbows and the lateral basins connected to the watercourses. They tolerate the warm and often poor in oxygen waters. Like the other Lepisosteidae, in fact they have a highly vascularized swim bladder that operates also as a breathing organ and allows them to ingest atmospheric air at the surface. This characteristic allows the species to survive in environments where the concentration of dissolved oxygen may get too low, especially during the warm periods and in the stagnant waters.
To retain prey: the jaws are armed with rows of long, pointed, conical teeth, often sold as alligator teeth © hambell
It is a large ambush predator. Often it keeps motionless among the vegetation, close to the banks or in the calm waters, and captures with a rapid start mainly fishes, but also crustaceans and other aquatic animals. The biggest individuals may prey upon even small vertebrates that get closer to the surface of the water. The typical armour of ganoid, rhomboidal and covered by a very hard substance similar to dentine scales, provides an effective protection against several predators. Also the skull is heavily ossified and contributes to the primitive and armoured appearance of the animal.
Morphophysiology
Atractosteus spatula stands among the biggest freshwater animals nowadays existing and is the largest of the extant Lepisosteidae. It may exceed 3 m in length and attain a weight exceeding 140 kg. even if the specimens having such dimensions are exceptional. The body is elongated and cylindrical, covered by the characteristic ganoid scales arranged in regular rows. The head is massive with and relatively wide and short if compared to other Lepisosteidae, so much so as to remind that of an alligator. The jaws are armed with numerous conical, long and pointed teeth particularly suitable for holding the prey. On the upper jaw are present two rows of quite similar teeth, that in some instances are even marketed as alligator teeth. The eyes are relatively small and located in the upper part of the head, a characteristic useful for a predator that may stay almost completely sunken thus observing what is going on in the vicinity of the surface.
Swimming at the surface, it can use its highly vascularized swim bladder to breathe and ambush prey, motionless like a floating log © RJ Baltierra
The dorsal and the anal fins are set very far back and placed very close to the caudal, imparting to the body a look particularly similar to that of the big fossil fishes. The caudal fin is heterocercal, with the upper lobe extended posteriorly. The dorsal and the anal fins often do have some blackish mimetic patches, whilst the showy pelvic and pectoral fins are mostly uniformly dark. Usually the livery is olive-brown on the back and the sides and gets progressively paler towards the belly.
Like in the other Lepisosteidae, the large scales are very hard and resistant. Their particular structure has allowed these fishes to maintain a substantially archaic morphology that kept recognizable all over millions of years of evolution.
Ethology-Reproductive Biology
The adults conduct a usually solitary life, especially outside the reproductive season, and can keep motionless for long periods waiting for a prey to get close. Hunting occurs mainly by ambush: the fish suddenly darts forward and seizes the victim with its long jaws amed with teeth. To reproduce, the Alligator gars gather in spring in the alluvial plains, in the shallower and rich aquatic vegetation zones, where the eggs are spawned. Reproduction is strictly linked to spring floods: the rise in water level allows the adults to reach areas temporarily flooded that form particularly favourable environments to the development of the progeny.
Atractosteus spatula breeds in spring on floodplains, in shallow waters rich in aquatic vegetation. The eggs are poisonous and thus rarely preyed upon © Giuseppe Mazza
The eggs are spawned on the submerged vegetation and are very numerous. Furthermore, they are toxic if ingested, a characteristic that is an important natural defence against several predators. After hatching, the larvae remain initially anchored on the vegetation by means of an adhesive structure present on the head and complete the development of the first phase of their life utilizing the resources of the yolk sac.
Growth is relatively rapid during the first years, whilst sexual maturity is attained quite late. This combination of growth, longevity and late reproduction renders the species particularly sensitive to adults’ mortality and therefore to fishing pressure. In fact the resilience of the species is very low, with a minimum time estimated of about 14 years for doubling the populations. Fishing represents one of the main anthropic pressures, also through particular sport techniques, like fishing with bow and arrows. Despite these characteristics, from 2025, considering its ample range of distribution, estimated in the order of 200.000-2.500.000 km², Atractosteus spatula appears as “LC, Least Concern“, in the IUCN Red List of the endangered species.
Synonyms
Lepisosteus spatula Lacépède, 1803; Litholepis adamantinus Rafinesque, 1818; Atractosteus adamantinus (Rafinesque, 1818); Lepisosteus ferox Rafinesque, 1820; Lepisosteus berlandieri Girard, 1858; Atractosteus lucius Duméril, 1870.
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