Blue catfish in the context of "Lake Moultrie"

Catfish (or catfishes; order Siluriformes /sɪˈljʊərɪfɔːrmiːz/ or Nematognathi) are a diverse group of ray-finned fish. Catfish are named for their prominent barbels, which resemble a cat's whiskers, though not all catfish have prominent barbels. All siluriformes lack scales, including both the armour-plated and naked species. This order of fish are defined by features of the skull and swimbladder. 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 detritivorous and scavenging bottom feeders, down to the tiny ectoparasitic species known as the candiru.

In the Southern United States, catfish may be known by a variety of slang names, such as "mud cat", "polliwogs", or "chuckleheads". Such names are regional and unstandardized. For instance, "chucklehead" in one region may refer to a bullhead catfish but indicate blue catfish elsewhere.

Ameiurus is a genus of catfishes in the family Ictaluridae. It contains the three common types of bullhead catfish found in waters of the United States, the black bullhead (Ameiurus melas), the brown bullhead (Ameiurus nebulosus), and the yellow bullhead (Ameiurus natalis), as well as other species, such as the white catfish (Ameiurus catus or Ictalurus catus), which are not typically called "bullheads".

The species known as bullheads can be distinguished from channel catfish and blue catfish by their squared tailfins, rather than forked.