CATFISH, the name generally given to the fishes of the sub order Siluroidea of the order Ostariophysi, in which the air-bladder is connected with the internal ear by a chain of ossicles, probably enabling the fishes to hear well. From the Cyprinoids (characins, carps and electric eels) the Siluroids are distinguished by having the body naked or armoured with bony plates, never normally scaled, and by a number of osteological characters : the air-bladder generally extends laterally so that on each side it is in contact with the skin above the pectoral fin. The name "cat-fish" has reference to the long barbels or feelers about the mouth, of which one pair supported by the maxillaries is always present ; generally there are two pairs below the chin, and frequently another developed from the valves between the nostrils. Nearly all the Siluroids are fresh water fishes, but two families are secondarily marine, the Ariidae, found on the coasts and in estuaries of all tropical countries, and the Plotosidae of the Indo-Pacific. The group is a large and varied one, containing probably about 2,000 species belonging to 23 different families; most are omnivorous, feeding on almost any kind of animal or vegetable food, and acting as scavengers.
The spines of the dorsal and pec toral fins, which are so generally present, are powerful weapons, capable of inflicting severe and sometimes poisonous wounds.
The cat-fishes of North Amer ica belong to the family Amiuri dae, which is peculiar to that con tinent except for a species in China, and is known also from fresh-water deposits in Wyoming of middle Eocene age. The Amiuridae are closely related to the Bagridae of Africa and Asia, and like them and most Siluroids have a short dorsal fin, with a spine, followed by an adipose fin on the tail. The anterior rays of the pectoral fins are spinous. The head is rather flat, with the mouth terminal and moderately wide, and the jaws with bands of small teeth; there are eight barbels. There are about 25 species, some of which are small; Amiurus lacustris of the Great Lakes attains a weight of more than r solb. These fishes scoop out a nest in the mud, and the male parent guards the eggs, and later swims with the brood near the shore.
The European cat-fish (Silures glanis), the "Wels" of the Ger mans, is said to reach a length of i oft. and a weight of 400 lbs. It has a very long tail, beneath which is the long anal fin. Another species (Parusilurus aristotelis) occurs in Greece ; the remaining Siluridae are Asiatic. In South and Central America are no less than nine families of Siluroids, all endemic. Diplomyste of Chile and Argentina, with toothed maxillary, is the most primitive living Siluroid, but other South American forms are highly specialized. Of the Aspredinidae, Aspredo batrachus is remarkable for the way in which the female carries the eggs on the abdomen ; these sink into the soft spongy skin and a cup develops round each and then becomes stalked. The Trichomycteridae include Stego philus and Vandellia, little slender naked fishes that live parasitically in the gill chambers of other fishes, and are said to enter the urethra of persons bathing, and by distending the short spines with which the gill-covers are armed, to cause inflammation or even death.
The Loricariidae, with about 30o species, are mostly fishes that are covered by a long armour of five series of bony plates on each side, and have the lips expanded into a sucker by means of which they hold on to stones. They feed mainly on mud and algae and have a very long intestine that is coiled like a watch-spring. In some species there are pronounced sexual differences, the males having broader and blunter heads, margined with spines or bristles, or bearing branched tentacles on the snout. In the mountain streams of the Andes the Loricariidae are represented by small forms (Cyclopium or Arges) known as "prenadillas"; in these regions there are no carnivorous fishes to attack them and they are completely naked, having lost the bony armour that pro tects the lowland forms. A mining engineer who had diverted a stream in order to empty a pot-hole, observed a number of these fishes climb a precipice from the hole to the stream above it, ob taining alternate holds with the sucker and the rough surface of the pelvic fins ; these were moved forward by the contraction of special muscles attached to the pelvic bones, while the sucker was holding. The Callichtyidae are another armoured family, but with only two rows of plates on each side of the body. Callichthys builds nests of grass, sometimes placed in a hole scooped out of the bank; both parents guard the nest. In the South American Doradidae, as in the similar but unrelated Mochochidae of Africa, the air-bladder is a sound-producing organ. Doras travels from one pond to another in the dry season, sometimes journeying all night. The Clariidae of Africa and Asia are also air-breathing fishes, provided with air-chambers above the gills ; in Clarias special vas cular tree-like organs nearly fill the chamber, but in Saccobran chus these are absent and the air-sac extends backwards for half the length of the fish. These are elongate, more or less eel shaped fishes ; in the dry season they burrow in the mud, but some species are said to leave their burrows at night and crawl about on land in search of food.
The African Amphiliidae and the Sisoridae of India have the lower surface of the head and abdomen flat and the paired fins horizontal, an adaptation to life in mountain torrents; in some genera the lips form a sucker similar to that of the Loricariidae. The electric cat-fish (Malopterurus electricus) is widely dis tributed in Africa. The skin is soft, and immediately beneath it lies the electric organ, formed of rhomboidal cells of a fine gelatinous substance, and differing from that of other fishes in being part of the tegumentary system, not derived from the muscles. Certain species of Synodontis, a genus common in the Nile, are white on the back and blackish beneath, a coloration con nected with their habit of swimming belly upwards. The Ariidae, most of which live in salt water, are typical Siiuroids in form and structure of the fins, whereas the other marine family, the Plotosidae, have a very long tail, with the long anal fin confluent with the caudal. In some species of Aris the eggs, few in number and as large as marbles, are carried about by the male in his mouth. Bucklandium from the lower Eocene (London clay) is an Ariid. (C. T. R.)