Page:EB1911 - Volume 05.djvu/532

 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).



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.



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