Hypostomus agna

Hypostomus agna is a species of catfish in the family Loricariidae. It is native to South America, where it occurs in the Ribeira de Iguape River basin. It was formally described as a new species in 1907 by Brazilian ichthyologist Alípio de Miranda-Ribeiro, as a species of Plecostomus.

The species reaches 22 cm (8.7 inches) in total length and is thought to be a facultative air-breather. Its keels are absent or poorly developed. The caudal peduncle has a trapezoidal shape in cross-section. These two features are used to distinguish it between closely related species also present in the Ribeira de Iguape river basin.