Hoplias, the trahiras or wolf fish, is a genus of large, predatory characins in family Erythrinidae, widespread across Central and South American freshwaters, with atlas records from Brazil, Argentina, Venezuela, Guyana, Suriname, Colombia, Costa Rica, and French Guiana. Atlas species range from a substantial 6 in up to roughly a metre for the largest species, the aimara (H. aimara) - heavy-bodied, elongate ambush predators with a large, tooth-studded mouth built to strike fast-moving prey from cover, including fish, crustaceans, and small vertebrates.
Trahiras are mostly a fisheries and scientific-interest genus rather than a mainstream aquarium fish - the aimara in particular is a well-known sport and food fish in Guiana Shield rivers. A handful of Hoplias reach the specialist predator-keeping hobby, but their large adult size, aggression, and strictly predatory diet make them unsuitable for typical community tanks. The genus has also seen active taxonomic revision in recent decades, with the widespread nominal species H. malabaricus long recognized as masking a cluster of closely related, hard-to-distinguish lineages. Conservation data lean toward Least Concern where assessed, though more than half the atlas's 15 species are still Not Evaluated.