1911 Encyclopædia Britannica/Cat-fish

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CAT-FISH, the name usually applied to the fishes of the family Siluridae, in allusion to the long barbels or feelers about the mouth, which have been compared to the whiskers of a cat. The Siluridae are a large and varied group, mostly inhabitants of fresh waters; some of them by their singular form and armature are suggestive of the Devonian mailed fishes, and were placed at one time in their vicinity by L. Agassiz. Even such authorities as T. H. Huxley and E. D. Cope were inclined to ascribe ganoid affinities to the Siluridae; but this view has gradually lost ground, and most modern ichthyologists, if not all, have adopted the conclusions of M. Sagemehl, who has placed the Siluridae near the carps and Characinids in the group Ostariophysi. The Silurids and Cyprinids may be regarded as two parallel series derived from some common stock which cannot have been very different from the existing Characinids. In spite of the archaic appearance of some of its members, the family Siluridae does not appear to extend far back in time, its oldest known representative being the Bucklandium diluvii of the Lower Eocene (London Clay) of Sheppey. A great number of forms were placed by Cuvier and his successors in the family Siluridae, which has since been broken up by T. Gill and other American authors into several families, united under the name of Nematognathi. A middle course appears the more reasonable to the present writer, who has divided the Siluridae of Cuvier into three families, with the following definitions:—
Siluridae—ribs attached to strong parapophyses; operculum well developed.
Loricariidae—ribs sessile; parapophyses absent; operculum more or less developed.
Aspredinidae—ribs sessile; strong parapophyses; operculum absent.

These three families may be defined among the Ostariophysi by having the parietal bones fused with the supraoccipital, no symplectic, the body naked or with bony scutes, the mouth usually toothed, with barbels, and usually an adipose dorsal fin.

The Siluridae embrace more than one thousand species, spread over the fresh waters of all parts of the world, but mostly from between the tropics. They are absent from western Europe and north-west Africa, and from North America west of the Rocky Mountains, but this deficiency has been made good by now, the introduction of Amiurus nebulosus and allied species in various parts of continental Europe and California having proved a success. Only a few forms are marine (Plotosus, Arius, Galeichthys).

EB1911 Cat-fish Fig. 1 The 'Wels' (Siluris glanis).jpg
 Fig. 1.—The “Wels” (Silurus glanis).

The species which has given the name to the whole family is the “Wels” of the Germans, Silurus glanis, the largest European fresh-water fish, inhabiting the greater part of Europe from the Rhine eastwards and north of the Alps. Its head is large and broad, its mouth wide, furnished with six barbels, of which those of the upper jaw are very long. Both jaws and the palate are armed with broad bands of small closely-set teeth, which give the bones a rasp-like appearance. The eyes are exceedingly small. The short body terminates in a long, compressed, muscular tail, and the whole fish is covered with a smooth, scaleless, slippery skin. Specimens of 4 and 5 ft. in length, and of 50 to 80 ℔ in weight, are of common occurrence, and the fish grows to 10 ft., with a weight of 400 ℔, in the Danube. Its food consists chiefly of other bottom-feeding fishes, and in inland countries it is considered one of the better class of food fishes. Stories about children having been found in the stomach of very large individuals are probably inventions. An allied species (S. aristotelis) is found in Greece.

The Clarias and Heterobranchus of Africa and south-eastern Asia have an elongate, more or less eel-shaped body, with long dorsal and anal fins, and are known to be able to live a long time out of water, being provided with an accessory dendritic breathing organ situated above the gills. Some species live in burrows during the dry season, crawling about at night in search of food. The common Nile species, the “Harmoot” (Clarias lazera), occurs abundantly in the Lake of Galilee and was included in, if not chiefly aimed at, by the Mosaic law which forbade the Jews to eat scaleless fishes, a prohibition which has been extended to eels in spite of the obvious presence of minute scales in the latter.

The Saccobranchus of India and Ceylon, a genus more nearly related to Silurus, have also an accessory organ for breathing atmospheric air. It consists of a long sac behind the gill-cavity, extending far back on each side of the body under the muscles.

In the majority of the Siluridae, called by A. Gunther the Proteropterae, a section extremely numerous in species, and represented throughout the tropics, the dorsal fin consists of a short-rayed and an adipose portion, the former belonging to the abdominal vertebral column; the anal is always much shorter than the tail. The gill-membranes are not confluent with the skin of the isthmus; they have a free posterior margin. When a nasal barbel is present, it belongs to the posterior nostril. This section includes among many others the genus Bagrus, of which the bayad (B. bayad) and docmac (B. docmac) frequently come under the notice of travellers on the Nile; they grow to a length of 5 ft. and are eaten.

Of the “cat-fishes” of North America (Amiurus), locally called “bull-heads” or “horned-pouts,” with eight barbels, some twenty species are known. Some of them are valued as food, especially one which is abundant in the ponds of New England, and capable of easy introduction into other localities (A. nebulosus). Others which inhabit the great lakes (A. nigricans) and the Mississippi (A. ponderosus) often exceed the weight of 100 ℔ Platystoma and Pimelodus people the rivers and lakes of tropical America, and many of them are conspicuous in this fauna by the ornamentation of their body, by long spatulate snouts, and by their great size.

The genus Arius is composed of a great number of species and has the widest distribution of all Silurids, being represented in almost all tropical countries which are drained by large rivers. Most of the species live in salt water. They possess six barbels, and their head is extensively osseous on its upper surface; their dorsal and pectoral spines are generally developed into powerful weapons. Bagarius, one of the largest Silurids of the rivers of India and Java, exceeding a length of 6 ft., differs from Arius in having eight barbels and the head covered with skin.

R. Semon has made observations in Queensland on the habits of Arius australis, which builds nests in the sandy bed of the Burnett river. These nests consist of circular basin-like excavations about 20 in. in diameter, at the bottom of which the eggs are laid and covered over by several layers of large stones. In the marine and estuarine species of Arius, Galcichthys and Osteogeniosus, the male, more rarely the female, carries the eggs in the mouth and pharynx; these eggs, few in number, are remarkably large, measuring as much as 17 or 18 millimetres in diameter in Arius commusonii, a fish 3 or 4 ft. in length.

The common North American Amiurus nebulosus also takes care of its eggs, which are deposited beneath protecting objects at the bottom of the water, failing which both parents join in excavating a sort of nest in the mud. The male watches over the eggs, and later leads the young in great schools near the shore, seemingly caring for them as the hen for her chickens.

EB1911 Cat-fish Fig. 2.—Synodonus xiphias.jpg
 Fig. 2.—Synodonus xiphias.

In the Siluridae Stenobranchiae of Gunther the dorsal fin consists of an adipose portion and a short-rayed fin which belongs to the abdominal vertebral column, and, like the adipose fin, may be sometimes absent. The gill-membranes are confluent with the skin of the isthmus. The Silurids belonging to this section are either South American or African. Among the former we notice specially the genus Doras, which is distinguished by having a series of bony scutes along the middle of the side. The narrowness of their gill-openings appears to have developed in them a habit which has excited the attention of all naturalists who have visited the countries bordering upon the Atlantic rivers of tropical America, viz. the habit of travelling during seasons of drought from a piece of water about to dry up to ponds of greater capacity. These journeys are occasionally of such a length that the fish have to travel all night; they are so numerous that the Indians fill many baskets of them. J. Hancock supposes that the fish carry a small supply of water with them in their gill-cavity, which they can easily retain by closing their branchial apertures. The same naturalist adds that they make regular nests, in which they cover up their eggs with care and defend them—male and female uniting in this parental duty until the eggs are hatched. Synodontis is an African genus and common in the Nile, where the various species are known by the name of “Shal.” They frequently occur among the representations of animals left by the ancient Egyptians. The upper part of their head is protected by strong osseous scutes, and both the dorsal and pectoral fins are armed with powerful spines. Their mouth is small, surrounded by six barbels, which are more or less fringed with a membrane or with branched tentacles.

EB1911 Cat-fish Fig. 3.—Malopterurus electricus.jpg
 Fig. 3.—Malopterurus electricus.

The curious fact of some species of Synodontis having the lower parts darker than the upper, some being whitish above and blackish beneath, appears to be connected with their habit of swimming in a reversed position, the belly turned upwards. This habit, known to the ancient Egyptians, who have frequently represented them in that attitude, has been described by E. Geoffrey, who says they nearly constantly swim on their back, moving quite freely forwards and sidewards; but if alarmed, they revert to the normal position to escape more rapidly.

The electric cat- or sheath-fishes (Malopterurus) have been referred to the same section. Externally they are at once recognized by the absence of a rayed dorsal fin, of which only a rudiment remains as a small interneural spine concealed below the skin. The entire fish is covered with soft, villose skin, an osseous defensive armour having become unnecessary in consequence of the development of a powerful electric apparatus, the strength of which, however, is exceeded by that of the electric eel and the large species of Torpedo.

The electric organ of Malopterurus differs essentially from that of other fishes provided with such batteries, being part of the tegumentary system instead of being derived from the muscles. It consists of rhomboidal cells of a fine gelatinous substance immediately under the skin. It is put into action by a single ganglionic cell at the anterior extremity of the spinal cord. Contrary to what takes place in other electric fishes, the current proceeds from the head to the tail.

The electric cat-fish, which grows to a length of 3 ft. in the Congo, has a wide distribution in Africa, extending from the Nile to the Zambezi and from the Senegal to the Congo. It was well known to the ancient Egyptians, who have depicted it in their mural paintings and elsewhere, and an account of its electric properties was given by an Arab physician of the 12th century; then as now the fish was known under the suggestive name of Raad or Raash, which means “thunder.”

Günther’s Siluridae Branchicolae comprise the smallest and least developed members of the family; they are referred to two genera only from South America, Stegophilus and Vandellia, the smallest of which does not exceed the length of 2 in. Their body is soft, narrow, cylindrical and elongate; the dorsal and anal fins short; the vent far behind the middle of the length of the body; gill-membranes confluent with the skin of the isthmus. Each maxillary is provided with a small barbel; and the gill-covers are armed with short stiff spines. Their small size notwithstanding, these Silurids are well known to the Brazilians, who accuse them of entering and ascending the urethra of persons while bathing, causing inflammation and sometimes death. Some certainly live parasitically in the gill-cavity of large Silurids, and F. Silvestri has observed Stegophilus insidiosus to suck the blood in the gills of Platystoma coruscans, a Silurid growing to a length of 6 ft.

EB1911 Cat-fish Fig. 4.—Callichthys armatus.jpg
 Fig. 4.—Callichthys armatus, from the upper Amazons.

The mailed cat-fish of the South American genus Callichthys builds regular nests of grass on leaves, sometimes placed in a hole scooped out in the bank, in which they cover their eggs and defend them, male and female sharing in this parental duty. In the allied Corydoras a lengthy courtship takes place, followed by an embrace, during which the female receives the seminal fluid in a sort of pouch formed by the folded membranes of her ventral fins; immediately after, five or six eggs are produced and received in the pouch, to be afterwards carefully placed in a secluded spot. This operation is repeated many times, until the total number of eggs, about 250, have been deposited. In accordance with these pairing habits, the pectoral spines of the male, which are used in amplexation, are larger and stronger than those of the female. These fish are monogamous, and both parents remain by the side of the nest, furiously attacking any assailant.

EB1911 Cat-fish Fig. 5.—Loricaria lanceolata.jpg
 Fig. 5.—Loricaria lanceolata, from the upper Amazons.

The allied family Loricariidae is entirely confined to the fresh waters of Central and South America. C. T. Regan, who has recently published an elaborate monograph of them, recognizes 189 species, referred to 17 genera. Many of them are completely mailed; but all have in common a short-rayed dorsal fin, with the ventrals below or rarely in front of it. Their gill-openings are reduced to a short slit. The first group of this section comprises alpine forms of the Andes, without any armature, and with a very broad and pendent lower lip. They have been referred to several genera (Stygogenes, Arges, Brontes, Astroblepus), but are collectively called “preñadillas” by the natives, who state that they live in subterranean craters within the bowels of the volcanoes of the Andes, and are ejected with streams of mud and water during eruptions. These fishes may, however, be found in surface waters at all times, and their appearance in great quantities in the low country during volcanic eruptions can be accounted for by numbers being killed by the sulphuretted gases which escape during an eruption and by their being swept down with the torrents of water issuing from the volcano. The lowland forms have their body encased in large scutes, either rough, scale-like, and arranged in four or five series (Chaetostomus), or polished, forming broad rings round the slender and depressed tail (Loricaria, fig. 5). They are mostly of small size.

EB1911 Cat-fish Fig. 6.—Abdomen of Aspredo batrachus.jpg
 Fig. 6.—Abdomen of Aspredo batrachus, with the ova attached;
 at a the ova are removed, to show the spongy structure of the skin,
 and the processes filling the interspaces between the ova.

In certain of the mailed genera the secondary sexual differences may be very pronounced, and have given rise to many nominal species. The shape of the snout may differ according to the sex, and its margin may be beset with tentacles in the male, whilst it frequently happens that the head of the latter is margined with spines or bristles which are either absent or considerably shorter in the female.

The Aspredinidae, which are also closely related to the Siluridae, are represented by four genera and eighteen species from South America. Aspredo batrachus (fig. 6), of the Guianas, the largest form, reaching to about a foot in length, deserves notice from the manner in which the female carries her eggs attached to the belly and paired fins, in a single layer, each egg being connected with the skin by a cup-shaped pedunculate base supplied with blood-vessels and coated with a layer of epithelium, the formation of which is still unexplained.  (G. A. B.)