Fish belonging to the order Siluriformes, in which barbels (feelers) on the head are well-developed, so giving a resemblance to the whiskers of a cat. Catfishes are found worldwide, mainly but not exclusively in fresh water, and are plentiful in South America.

The Eastern European giant catfish or wels Silurus glanis grows to 1.5 m/5 ft long or more. It has been introduced to several places in Britain. The unrelated marine wolffish Anarhicas lupus, a deep-sea relative of the blenny, growing 1.2 m/4 ft long, is sometimes called a catfish.