Hoplosternum is a genus of armored catfish (family Callichthyidae) from South America, recorded in the atlas from Colombia, Venezuela, Argentina, Bolivia, Brazil, Ecuador, French Guiana and Guyana — a wide swath of the continent's lowland floodplains and swamps. Like their smaller relatives the Corydoras, Hoplosternum have two rows of bony plates running along the flanks instead of scales, but they grow considerably larger, with the atlas covering 4 species from about 7 up to 10.5 in. A defining trait of the genus is accessory air-breathing: the fish gulp air at the surface and absorb oxygen through the hindgut, letting it survive stagnant, oxygen-poor water that would suffocate most other fish.
Hoplosternum littorale, generally known by the common name cascudo, is the best-studied member of the genus and the one most familiar to aquarists and to local fisheries alike across its range, historically an important food fish in seasonally flooded wetlands. The genus is also known for an unusual reproductive strategy: males build a floating bubble nest at the surface, often anchored to plant matter, and guard the eggs and fry there rather than depositing them on a fixed surface as Corydoras do. Conservation status looks generally secure — the atlas tally runs two Least Concern to one Near Threatened and one Not Evaluated — though the Near Threatened listing is a signal that wetland habitat loss is a live pressure somewhere in the genus's range.