Hoplerythrinus

Hoplerythrinus is a genus of freshwater fish belonging to the family Erythrinidae. The most well-known species in this genus is Hoplerythrinus unitaeniatus, commonly known as the redtail trahira or wolf fish. These fish are native to South America, found in the Amazon and Orinoco basins, as well as in other river systems in countries such as Brazil, Venezuela, and Colombia.

Hoplerythrinus are predatory fish, characterized by their elongated bodies and large mouths filled with sharp teeth. They are opportunistic hunters, feeding on smaller fish, amphibians, and invertebrates. Their coloration can vary, but they typically exhibit a brownish or grayish body with a distinctive reddish or orange caudal fin, which gives them one of their common names.

A notable characteristic of Hoplerythrinus is their ability to breathe atmospheric air. They possess a modified swim bladder that functions as a lung, allowing them to survive in oxygen-poor environments or to venture out of the water for short periods. This adaptation is particularly useful during dry seasons when water levels can drop significantly.

In their natural habitat, Hoplerythrinus inhabit slow-moving waters, swamps, and flooded forests, often seeking cover among vegetation. They are also kept in aquariums by some enthusiasts, though their predatory nature and size potential require spacious and well-maintained tanks.