Hoplerythrinus is a genus of trahiras, or wolf fishes, in family Erythrinidae, a group of predatory Characiformes found across much of tropical South America. The atlas records the genus from French Guiana, Argentina, Bolivia, Brazil, Colombia, Guyana, Paraguay, and Peru, and its three species span 7–15.5 in. Like its erythrinid relatives, Hoplerythrinus has an elongated, cylindrical body, a large upward-angled mouth full of canine-like teeth, and a vascularized, lung-like extension of the swim bladder that lets it gulp air at the surface - an adaptation to the low-oxygen swamps, floodplain pools, and seasonally drying backwaters it favors.
The striped trahira (H. unitaeniatus) is the most widely distributed and best-documented of the three, tolerant of stagnant, weedy water and seasonal hypoxia that most fish avoid; Gronovius's wolf fish (H. gronovii) is the other named species in the atlas, alongside the more obscure H. cinereus. None of the three is a mainstream aquarium fish - they are solitary ambush predators that quickly outgrow all but very large tanks and need whole prey or large live or frozen foods - so interest tends to come from native-fish and predatory-fish specialists rather than the general hobby. Conservation data are thin across the genus: one atlas species is rated Least Concern, one Data Deficient, and one not yet formally evaluated.