Catfish are a diverse group of ray-finned fish. Named for their prominent barbels, which resemble a cat’s whiskers, catfish range in size and behavior from the three largest species alive, the Mekong giant catfish from Southeast Asia, the wels catfish of Eurasia, and the piraíba of South America, to detritivores (species that eat dead material on the bottom), and even to a tiny parasitic species commonly called the candiru, Vandellia cirrhosa. Neither the armour-plated types nor the naked types have scales. Despite their name, not all catfish have prominent barbels or “whiskers”. Members of the Siluriformes order are defined by features of the skull and swimbladder. Many of the smaller species, particularly the genus Corydoras, are important in the aquarium hobby. Many catfish are nocturnal, but others are crepuscular or diurnal.

Many Hypancistrus are popular aquarium fish due to their small size and attractive coloration. Because of their more carnivorous diet, these fish are not like the algae eaters aquarists are used to.

Catfish are usually bottom feeders and therefore usually are purchased to perform some sort of function in terms of fish tank maintenance. Soft, relatively acidic water is preferred.