SHARK, a Selachian fish (see ), belonging to the
order Plagiostomi, suborder Squali.
Sharks are almost exclusively inhabitants of the sea, but some
species enter the mouths of large rivers, and one species
(Carcharias gangeticus) occurs frequently high up in the large rivers
of India. C. nicaraguensis of the lake of Nicaragua and the Rio
San Juan appears to have taken up its residence permanently
in fresh water. Sharks are most numerous between the tropics, a few only reaching the Arctic circle; it is not known how far they advance S. in the Antarctic region. Altogether some hundred and fifty different species have been described.
With regard to their habits many are littoral species, the
majority pelagic, and a few are known to belong to the deep-sea
fauna, having hitherto been obtained down to a depth of nearly
1000 fathoms.
Littoral Sharks. — The littoral forms are of small size, and
generally known under the name of “dog-fishes,” “hounds,” &c. Some pelagic sharks of larger size also live near the shore on certain parts of a coast, but they are attracted to it by the abundance of food, and are as frequently found in the open sea, which is their birthplace; therefore we shall refer to them when we speak of the pelagic kinds.
The majority of the littoral species live on the bottom, sometimes
close inshore, and feed on small marine animals or on any
animal substance. The following are deserving of special notice.
The tope (Galeus) is common on the coasts not only of England, Ireland and of S. Europe, but also of S. Africa, California, Tasmania and New Zealand. Its teeth are equal in both jaws, of rather small size, flat, triangular, with the point directed towards the one side, and with a notch and denticulations on the shorter side (fig. 1). It is of a uniform slaty-grey colour, and attains to a length of 6 ft. The female brings forth some thirty living young at one birth in May. It becomes troublesome at times to fishermen by taking their bait and driving away other fish they desire to catch. The fins of G. zyopterus of the Californian coast are much esteemed for culinary purposes by the Chinese.
The hounds proper (Mustelus) possess a very different dentition, the teeth being small, obtuse, numerous, arranged in several rows like pavement (fig. 2). Five or six species are known from the shores of the various temperate and subtropical seas, one (M. vulgaris) being common on the coasts of Great Britain and the United States, on the Pacific as well as the Atlantic side. It is of a uniform grey colour or sparingly spotted with white, and attains to a length of 3 or
4 ft. The young, about twelve in number, are brought forth
alive in November. It is comparatively harmless and feeds on
shells, crustaceans and decomposing animal substances.
The dogfishes proper (Scyllium, Chttoscyllium, &c.) are spread
over nearly all the temperate and tropical seas. Their teeth are
small, in several series, with a longer pointed cusp in the middle, and generally one or two smaller ones on each side (figs. 3 and 5). They are all oviparous, their oblong egg-shells being produced at each corner into a long thread by which the egg is fastened to some fixed object. Some of the tropical species are ornamented with a pretty pattern of coloration. The two British species, the lesser and the larger spotted dogfish (Sc. canicula and Sc. catulus), belong to the most common fishes of the coast and are often confounded with each other. But the former is finely dotted with brown above, the latter having the same parts covered with larger rounded brown spots, some of which are nearly as large as the eye. As regards size, the latter exceeds somewhat the other species, attaining to a length of 4 ft. Dogfishes may become extremely troublesome by the large numbers in which they congregate at fishing stations; they are rarely used as food, except in the Mediterranean countries, in China and Japan, and in the Orkneys, where they are dried for home consumption. The black-mouthed dogfish (Pristiurus melanostomus) is rarely caught on the British coasts, and is recognized
by a series of small, flat spines with which each side of the upper
edge of the caudal fin is armed.
4 — Chiloscyllium trispeculare.