Catfish are any of about 31 families and 2,000 species of fish belonging to the order Siluriformes, most of which are found in freshwater. Distributed throughout the world, they are most diverse in South America.
Catfish are distinguished by the presence of barbels, or "whiskers"; the lack of true scales; strong spines at the front of the dorsal and pectoral fins; and, in most cases, an adipose fin on top of the body, in front of the caudal fin. The body is usually partly to completely armored.
Most catfish have small eyes and therefore rely on taste, smell and hearing. The barbels and much of the skin are often covered with tastebuds. Many catfish are inactive during the day, coming out to feed at night. Freshwater catfish usually spend much of their time (and lay their eggs) in hollow logs, undercut banks and other hiding places; if these are removed, catfish populations decline.
One or both parents guard the eggs until they hatch. The eggs are usually large, 2 to 10 mm (0.1 to 0.4 inches) in diameter; males of some marine catfish species brood their eggs in the mouth. Many species of freshwater catfish are used for human food. North American catfish of the genus Ictalurus are important commercially and are popular with anglers.
Catfish farming, which involves raising and marketing such species as the channel catfish, I. punctatus, is a rapidly growing business in the Ssouthern United States. North American catfishes are fairly typical; others, however, are more distinctive in appearance or behavior. A parasitic catfish, the candiru, Vandellis cirrhosa, a minute South American catfish with strong, recurved spines, has been known to enter the urinary tract of persons wading in the water. The electric catfish, Malapterurus electricus, native to Africa, is capable of producing an electric charge of up to 350 volts, enough to stun a human.
The predatory walking catfish, Clarias batrachus, has lunglike organs that allow it to breathe air; this ability enables it to move over land from one body of water to another. Imported to the United States as a curiosity from Asia, walking catfish have escaped into rivers in southern Florida and have replaced native fish in some local waters. A European catfish, the wels, Silurus glanis, is one of the largest freshwater fishes; it may reach a length of 4.5 m (15 ft) and a weight of 300 kg (660 lb).
