Bucktooth Tetra

The bucktooth tetra has an elongated, laterally compressed body and a forked caudal fin. It attains a maximum standard length of 7.5 cm (3.0 in). There is a black line which extends from the operculum to the caudal peduncle; this joins two black blotches, one near the middle of the body and the other near the caudal peduncle. The background colour is iridescent silver, which can flash green, yellow or red, with yellow, orange-tipped fins. This species has larger teeth, although they do not live up to the species' common name, but the lips are more serrated than most characins'. They have well developed jaws equipped with pointed teeth; they are cuspid outward projecting pointed tips, an adaptation for their preferred food, the scales of other fishes. The bucktooth tetra is sexually dimorphic, with the males being distinguished from the females by having the fin rays in the dorsal and anal fins elongated and being slimmer than the females.

The bucktooth tetra is found in South America, where it has a wide but rather disjunct distribution. It has been recorded from the Araguaia, Tocantins, Orinoco, Río Branco, and upper Essequibo River basins in Brazil, Colombia, Guyana and Venezuela. It is normally found in shallow, sandy bottomed areas of rivers, as well as at rapids. The rivers this species are found in are typically flowing through savannas and grasslands.

The bucktooth tetra is the only species in the genus Exodon. Its name combines exo, meaning "outer" or "external", with odon, meaning tooth, referring to the teeth projecting out. The specific name, paradoxus, means "strange" or "against expectations", also thought to be a reference to the teeth projecting outwards.