Gnathocharax

Gnathocharax, is a monospecific genus of freshwater ray-finned fish belonging to the family Acestrorhynchidae, which includes the freshwater barracudas and the biting tetras. The only species in the genus is Gnathocharax steindachneri,^[2] also known as the arowana tetra.^[4] This fish is found in tropical freshwater habitats in the Orinoco and Amazon basins of South America.

Ganthocharax was first proposed as a genus in 1913 by the American zoologist Henry Weed Fowler when he described its only species, G. steindachneri.^[3] Fowler gave the type locality of this species as the Igarapé de Candelaria, a tributary of the Rio Madeira and about 2 miles (3.2 km) distant, at 8°45'S, 63°54'W, in Brazil.^[2] This taxon was formerly classified in the family Characidae, but is now classified within the subfamily Heterocharacinae, the small biting tetras, of the family Acestrorhynchidae,^[3] within the suborder Characoidei of the order Characiformes.^[5]

Ganthocharax combines gnáthos, meaning "jaw" in Greek, an allusion to the angled elongated maxilla, with charax, meaning a "palisade". Charax is a reference to this fish's dense, sharp teeth, and is a common element in the scientific names of characins. The specific name honours Franz Steindachner, the Austrian ichthyologist.^[6]

Gnathocharax has a maximum standard length of 5 cm (2.0 in).^[7] This taxon has a thin, laterally compressed body. Both jaws have prominent, protruding teeth, and the mouth points upwards. The background colour is silvery witha greenish iridescence, with a black blotch with red spots on its anterior and posterior margins on the caudal peduncle. There is a red crescent around the eyes, and a scattering of small black spots on the otherwise transparent fins.^[8]

Gnathocharax is found in the drainages of the Amazon and Orinoco rivers, and has been recorded from Bolivia, Brazil, Colombia, Ecuador, Guyana, Peru and Venezuela.^[1]