251. The SHARKS and DOG-FISH (Squalus, Fig. 64) constitute a tribe of sea-fish noted for their voracity, and peculiarly characterized by having, instead of gills, from four to seven breathing apertures, of curved form, on each side of the neck.
They are found in all seas, and some of them are of enormous magnitude, measuring from twenty to thirty feet and upwards in length.
The skins of nearly all these animals, which are rough, with hard and minute prickles, are in frequent use for polishing wood, ivory, and even iron. Those of the larger species are cut into thongs and traces for carriages; and, in Norway, a sort of leather is prepared from them, which is employed for shoes and many other purposes. The skin of the Spotted Dog-fish (Squalus canicula) is converted into the well-known substance called shagreen, or chagreen. For this purpose it is extended on a board and covered with mustard seed; and, after having been exposed for several days to the effects of the weather, it is tanned. The best shagreen is imported from Constantinople. This is of brownish colour, and very hard; but when immersed in water, it becomes soft and pliable, and may be dyed of any colour. Shagreen is often counterfeited by preparing morocco leather in the same manner as the skins of the dog-fish. Such fraud may, however, easily be detected by the surface of the spurious manufacture peeling or scaling off, whilst that of the genuine article remains perfectly sound. Shagreen is employed principally to cover cases for mathematical instruments, and was formerly used for watch-cases and the covers of books. Sharks' fins are an article of trade from the Arabian and Persian gulfs to India, and thence to China: they are generally packed in bales weighing each about 700 pounds.
The flesh of all the species of sharks is hard, and in general unpleasant both to the smell and the taste; yet it is sometimes eaten by seamen, after having been macerated for a while in water to soften it. The eggs of sharks are also eaten. The livers of all the species yield a considerable quantity of oil, which is useful for burning and for other purposes. From the livers of some of the larger kinds as much as seven or eight butts of oil have been obtained, worth twenty or thirty pounds and upwards.
252. The SKATE (Raia batis, Fig. 72) is a species of ray of large size, with flat and somewhat diamond-shaped body, and the mouth on the under side: the teeth sharp, and a single row of spines in the tail.
It is found in almost every part of the European ocean.
No fish of its tribe is so excellent for the table as the skate, particularly when it is young and has not fed in a muddy part of the sea. The flesh is white and of good flavour, but is usually crimped before it is cooked. The best season for skate is from January to March; and from July to September. So great is the size which these fish sometimes attain, that Willoughby mentions one that would have served 120 men for dinner. In several parts of the Continent skate are salted and dried for sale. The fishermen also sometimes dry the stomach as an article of food; and extract from the liver a white and valuable kind of oil.
253. The THORNBACK (Raia clavata) is a species of ray, which differs from the skate chiefly in having blunt teeth, and a row of curved spines along the middle of the body and on the tail.
This is a very common fish near all the coasts of Britain.
The flesh of thornback is much inferior to that of the skate, yet it is sometimes eaten. That of the young ones, which have the denomination of maids, is however peculiarly excellent. The Norwegian fishermen catch thornbacks chiefly on account of their livers; from these they extract a considerable quantity of oil, which they sell with great advantage to strangers who frequent their harbours.