Sharks have no scales like those of other fishes; their integuments are covered with calcified papillæ which, under the microscope, show a structure similar to that of teeth. If the papillæ are small, pointed, and close set, the skin is called “shagreen;” rarely they are larger, appearing as bucklers or spines, of various sizes.
These fishes are exclusively carnivorous, and those armed with powerful cutting teeth are the most formidable tyrants of the ocean. They have been known to divide the body of a man in two at one bite, as if by the sweep of a sword. Some of the largest sharks, however, which are provided with very small teeth, are almost harmless, feeding on small fishes only or marine invertebrates. Others, particularly of the smaller kinds, commonly called “Dog-fishes,” have short or obtuse teeth, and feed on shells or any other animal substance. Sharks scent their food from a distance, being readily attracted by the smell of blood or decomposing bodies.
In China and Japan, and many other eastern countries, the smaller kinds of sharks are eaten. Sharks’ fins form in India and China a very important article of trade, the Chinese preparing from them gelatine, and using the better sorts for culinary purposes. The fins are obtained not exclusively from Sharks but also from Rays, and assorted in two kinds, viz. “white and black.” The white consist exclusively of the dorsal fins, which are on both sides of the same uniform light colour, and reputed to yield more gelatine than the other fins. The pectoral, ventral, and anal fins pass under the denomination of black fins; the caudal fin is not used. One of the principal places where shark fishery is practised as a profession is Kurrachee. Dr. Buist, writing in 1850 (“Proc. Zool. Soc.” 1850, p. 100), states that there are thirteen large boats, with crews of twelve men each, constantly employed in this pursuit; that the value of the fins sent to the market varies from 15,000 to 18,000 rupees; that one boat will sometimes capture at a draught as many as one hundred sharks of various sizes; and that the number total of sharks captured during the year amounts probably to not less than 40,000. Large quantities are imported from the African coast and the Arabian Gulf, and various ports on the coast of India. In the year 1845–46, 8770 cwt. of sharks’ fins were exported from Bombay to China.
First Family—Carchariidæ.
Eye with a nictitating membrane. Mouth crescent-shaped, inferior. Anal fin present. Two dorsal fins, the first opposite to the space between pectoral and ventral fins, without spine in front.
Carcharias.—Snout produced in the longitudinal axis of the body; mouth armed with a series of large flat triangular teeth, which have a smooth cutting or serrated edge. Spiracles absent. A transverse pit on the back of the tail, at the root of the caudal fin.
This genus comprises the true Sharks, common in the tropical, but less so in the temperate seas. Between thirty and forty different species have been distinguished, of which one of the most common is the “Blue Shark” (Carcharias glaucus). Individuals of from twelve to fifteen feet are of very common occurrence, but some of the species attain a much larger size, and a length of 25 and more feet. Fishes of this genus or of closely allied genera (Corax, Hemipristis) are not uncommon in the chalk and tertiary formations.
Galeocerdo.—Teeth large, flat, triangular, oblique, serrated on both edges, with a deep notch on the outer margin. Spiracles small. A pit on the tail, above and below, at the root of the caudal fin. Two notches on the under caudal border, one of them at the end of the spine.
Fig. 112.—Dentition of the Blue Shark (Carcharias glaucus); the single teeth are of the natural size.