Catfish, any of the fishes of the order Siluriformes. Catfishes are related to the characins, carp, and minnows (order Cypriniformes) and may be placed with them in the superorder. Some authorities, however, have regarded these groups as suborders, rather than a single order, and have classified them as the suborders Siluroidea (catfishes) and Cyprinoidea of the order Cypriniformes.

The name catfish refers to the long barbels, or feelers, which are present about the mouth of the fish and resemble cat whiskers. All catfishes have at least one pair of barbels, on the upper jaw; they may also have a pair on the snout and additional pairs on the chin. Many catfishes possess spines in front of the dorsal and pectoral fins. These spines may be associated with venom glands and can cause painful injuries to the unsuspecting. All catfishes are either naked or armored with bony plates; none has scales.

Catfishes vary considerably in size. Small species, such as the dwarf Corydoras, or miro cat, may be as little as 4 or 5 centimetres (1 1/2–2 inches) long, while the wels, a large, European species, maybe 4.5 meters (15 feet) in length and 300 kilograms (660 pounds) in weight. A number of the smaller species, especially those of the genusCorydoras, are popular aquarium fishes, while many of the larger catfishes are edible and used as food. Notable examples of the latter are the many North American foods and sports fishes of the family, among them the blue catfish, with a maximum length and weight of 1.5 meters and 68 kilograms, and the channel catfish, growing to about 1 meter and 12 kilograms.