SILURIDAE, a large family of freshwater Fishes, flourishing in the present epoch, and represented by a great variety of forms in all the tropical and temperate regions, many of them reaching back into the Tertiary age. The principal characters of this family (termed a "suborder" by some), its position in the system, its geographical distribution, and some of the most remark-able points in the structure and life-history of its members have been already sufficiently noticed under ICHTHYOLOGY, but we have here to notice more fully the sections into which it has been divided, and certain remarkable forms which were referred to nominally only in that article.
The modifications of the vertical fins, or rather the specialization of certain portions at the expense of others, and the greater or less extent of the branchial aperture form excellent characters for subdividing the Siluroids.
I. In the Siluridse Homalopterse the vertical fins are exceedingly long, occupying nearly the whole extent of the embryonal fin, and in one genus (Heterohranchus) a great part of the dorsal portion retains its embryonic character, being arayless adipose fin. All the Siluroids of this section belong to the fauna of the Old World and Australia. The rivers and lakes of tropical Africa harbour many species of the genera Clarias and Heterohranchus,those of the Nile being known under the name of " Carmoot." One of the Nilotic species, Clarias macracanthus, occurs abundantly in the Lake of Galilee, and, being a long, scaleless, eel-like fish of black colour, with eight long barbels round its broad mouth, was certainly included among those which the Jews were forbidden to eat by the Mosaic law. These fish grow to a length of from 4 to 6 feet, and are eaten by the natives of tropical Africa.
II. In the Siluridse Heteropterse the dorsal fin has almost or entirely disappeared; only its foremost portion and a small adipose remnant may be preserved; on the other hand
the anal portion is retained in its whole extent. The gill-membranes remain separate and overlap the isthmus. This section likewise belongs to the fauna of the Old World, and includes, among many others, the species which has given the name to the whole family, Silurus giants, the " Wels"
FIG. 1.The " Wels " (Silurus glanisj.
of the Germans. It is the only representative of the family in Europe, and with the exception of the sturgeon, is the largest freshwater fish of the Continent. It was known to Aristotle, who described it under the name of Glanis. It inhabits more the central and eastern portions of Europe than the western, being absent in Italy, Greece, southern Switzerland, France, and those parts of Germany which are drained by the Rhine and its affluents. In general appear-ance it somewhat resembles the burbot. 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 feet in length, and of 50 to 80 ft> in weight, are of common occurrence. 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.
III. The Siluridx Anomalopiterx are a small section from tropical America, in which the dorsal and adipose fins are very short and belong to the caudal vertebral column, while the anal is very long, and the gill-membranes are entirely separate, overlapping the isthmus.
IV. The Siluridae Proteropterx are 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 feet, and are eaten. Of the " Cat-Fishes " of North America (Ami-urns), 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. p/onderosus) often exceed the weight of 100 lb. Platysterna and Pirnelodus 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 the greatest number of species (about seventy), and has the widest distribution of all Siluroids, being represented in almost all tropical countries which are drained by large rivers. Some of the species enter 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 Siluroids of the rivers of India and Java, ex-ceeding a length of 6 feet, differs from Arius in having eight barbels, and the head covered with skin.
V. In the Siluridx Slenobranchix 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 Siluroids 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. 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
FIG. 2.Synodontis xiphias.
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. Finally, the Electric Cat- or Sheath-Fishes (Malapterurus) also belong to this section. Externally
FIG. 3.Malapterurus electricus.
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 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. It has been noticed in vol. xii. p. 650. Three species have been described from rivers of tropical Africa, of which one (M. electricus) occurs in the Nile; it rarely reaches a length of 4 feet.
VI. The section of Siluridx Proteropodes contains small forms, some of which are of interest by the degree of specialization to which they have attained in one or the other direction. 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; their pectorals and ventrals have assumed a horizontal position; and their vent is before, or not much behind, the middle of the length of the body. 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, Astroplebus), but are collectively called " prenadillas " 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 sur-face 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 (Cheetostomus), or polished, forming broad rings round the slender \ and depressed tail (Loricaria, fig. 4), or \ polished and large, so as to form two series only along the body and short tail ______ (Callichihys, fig. 5). In India this section is but sparsely represented, chiefly in mountain-streams, by small loach-like Siluroids, in which various kinds of peculiar apparatus are developed to enable them to hold on to stones, this preventing their being swept away by the current ; in Pseudecheneis the adhesive apparatus consists of transverse plaits of the skin on the thorax between the pectoral fins; in Ex-ostoma the mouth is modified into a sucto-rial organ, probably with the same func-tion. Finally, the South-American genus Aspredo, which is remarkable for the peculiar mode of protecting its eggs, as mentioned in vol. xii. p. 660, belongs also to this section.
VII. The small section of Siluridm Opisthopterss com-prises South-American forms, the majority of which inhabit waters at high altitudes up to 14,000 feet above the level of the sea. All have a short-rayed dorsal fin, placed above or behind the middle of the length of the body, above or behind the ventrals, which may be absent. Also the anal is short. The nostrils are remote from each other, and the gill-membranes are not confluent with the skin of the isthmus. These little fishes, of which Trichomycterus and Nematogenys are the principal genera, replace in the Andes the loaches of the northern hemisphere ; they resemble them in appearance and habits, and even in coloration, offering a striking illustration of the fact that similar forms of animals are produced under similar external physical conditions.
VIII. Finally, the Siluridee Branckicolx 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 inches. 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 Siluroids are well known to the Brazilians, who accuse them of entering and ascending the urethra of persons while bathing, causing inflammation and sometimes death. They certainly live parasitically in the gill-cavity of large Siluroids, probably entering those cavities for places of safety, but without drawing any nourishment from their hosts. (A. GU.)
The above article was written by: Albert Günther, M.D., Ph.D., F.R.S., author of The Study of Fishes.