Catfish include some 2,500 species of mostly freshwater fish characterized by two to four pairs of whiskers or barbels around their mouth. Many species have spines on the dorsal fins and near the gills. In some species these spines may contain poison.
Catfish belong to the bony fish order Siluriformes, and are mainly freshwater forms with representatives throughout the world. Most species of catfish lack scales, although some species are covered with heavy plates of tough, armored skin. Catfish tend to be hardy and a few species can survive for some time out of water as long as their skin is kept moist by an external layer of mucus.
A few species of catfish live in the oceans, such as the sea catfishes of the family Aridae which are found in tropical and subtropical seas, and in temperate waters during the summer. Catfish vary in size from the pygmy corydoras (Corydoras hastatus), about 0.8 in (2 cm) long, to the giant catfish (Pangasianodon giga) of southeastern Asia, which can exceed 7 ft (2.1 m) and weigh 250 lb (113 kg). This group also includes the glass catfish (Physailla pellucida), a popular aquarium fish.
North American freshwater catfish are found from Canada to Guatemala. They are often caught by rod and reel, have considerable commercial importance, and are also raised on fish farms. Catfish live in murky lakes and ponds, feeding on the bottom on both live and dead material. Catfish spawn around May and June. The parents prepare a nest in the mud or sand. After the eggs hatch the parents guard the nest and protect the young until they have developed enough to become independent.
The most abundant North American catfish are the bullheads, including: the black bullhead (Ictalurus melas), the brown bullhead (I. nebulosus), and the yellow bullhead (I. natali).
Bullheads are plentiful in streams and ponds of North America, from the Atlantic to the Pacific Oceans. Bullheads are thought to have spread naturally from western North America to the east. Adhesive bullhead eggs may have stuck to the legs and feet of aquatic migratory birds, and later washed off when the birds traveled to another pond, thus establishing new populations of these fish.
Rivalling the bullheads in commercial importance in some areas are the channel catfish (I. punctatus), the blue catfish (I. furcatus), the white catfish (I. catus), and the flathead catfish (Pylodictus olivaris). These species may reach 150 lb (68 kg), although they are usually smaller. Catfish farming is an increasing enterprise in the southern United States, with more than 100 million lb (45.4 million kg) of fish being produced annually.
The diet of the ictalurids is varied since they eat almost anything, dead or alive. People fishing for catfish often use a use "stink bait." Such bait can lure catfishes over a wide expanse. Catfish can detect the bait using the extensive sensory surface of their body and their long barbels.
Also included in the North American catfish family are the madtoms in the genus Noturus. These are small fish under 5 in (13 cm) in length. Madtoms have glands associated with spines which can inflict extremely painful stab wounds.
The Eurasian catfish family Siluridae includes the wels (Siluris glanis), which grows over 12 ft (3.7 m) long and weighs hundreds of pounds. At the other extreme in this family is the glass catfish (Kryptopterus bicirrhus) of southeastern Asia, which is only 4 in (10 cm) long. The skin and muscles of the glass catfish are transparent enough to display its viscera.
The catfish family Clariidae includes labyrinthic fishes which have evolved a special air-breathing apparatus, found anterior to the gills and equipped with numerous blood vessels. These catfish can stay out of water for an extended period of time as long as their skin is kept moist with mucus. Air-breathing catfish can live in stagnant, low-oxygen water that would be lethal to other species of fish.
The walking catfish (Clarius batrachus) of southeast Asia "walks" on dry land by performing snakelike movements, using its pectoral fins as props. In times of severe drought these catfish try to move overland to ponds containing water, or they may dig into the bottom of a pool and wait there for the return of the rains.
The talking catfish (Acanthodoras spinosissimus, family Doradidae) makes a croaking sound, especially when captured. These sounds result from air forced in and out of the swim bladder due to changes in pressure when the pectoral fins flap.
In Africa, electric catfish (Malapterurus electicus, family Malapteruridae) range in size from 8 in (20 cm) to 4 ft (1.2 m) and reach a weight of 50 lb (23 kg). These fish can produce a 100-volt shock followed by lesser shocks, which can stun large fish. In addition to predation and defense, the electrical impulses are used to navigate in turbid water. The electric organs are found along the body and tail, and are derived from glandular cells in the epidermis, rather than from the muscles as occurs in other species of electric fish.