Erythrinus is a genus of trahiras, or wolf fish - elongated, cylindrical predatory characiforms in family Erythrinidae, found across a wide stretch of tropical South America including Brazil, Colombia, Peru, Venezuela, Bolivia, Ecuador, French Guiana, and Guyana. Atlas species run a fairly narrow 7.5–8 in. Like its erythrinid relatives, Erythrinus has a large mouth armed with canine-like teeth, a mottled camouflage pattern suited to ambush hunting among vegetation, and an accessory air-breathing organ that lets it tolerate the low-oxygen, stagnant pools and swamps typical of its habitat - even surviving brief periods stranded out of water during the dry season.
E. erythrinus, the red wolf fish, is the species most likely to be seen outside scientific literature, turning up occasionally in the specialist predatory-fish hobby among keepers drawn to its air-breathing habit and sit-and-wait hunting style; it needs a large, secure tank and a diet of whole prey items rather than flake or pellet food, and is not a fish for a community aquarium. The rest of the genus - including E. kessleri, E. guavina, and E. palustris - is essentially unknown in the trade. Conservation status is mostly unassessed, with five of the six species Not Evaluated and one rated Least Concern, reflecting how little formal survey attention this swamp- and floodplain-dwelling genus has received.