DOG-FISH, a name applied to several species of the smaller sharks, and given in common with such names as hound and beagle, owing to the habit these fishes have of pursuing or hunting their prey in packs. The small-spotted dog-fish or rough hound (Scyllium canicula) and the large-spotted or nurse hound (Scyllium catulus) are also known as ground-sharks. They keep near the sea bottom, feeding chiefly on the smaller fishes and Crustacea, and causing great annoyance to the fishermen by the readiness with which they take bait. They differ from the majority of sharks, and resemble the rays in being oviparous. The eggs are enclosed in semi-transparent horny cases, known on the British coasts as "mermaids' purses," and these have tendril-like prolongations from each of the four corners, by means of which they are moored to sea-weed or some other fixed object near the shore, until the young dog-fish is ready to make its exit. The larger of these species attains a length of 4 to 5 ft., the smaller rarely more than 30 in. The picked dog-fish (Acanthias vulgaris, formerly known as Squalus acanthias) is pre-eminently the dog-fish. It is the most abundant of the British sharks, and occurs in the temperate seas of both northern, and southern hemispheres. It attains a length of 4 ft., but the usual length is 2 to 3 ft., the female, as in most sharks, being larger than the male. The body is round and tapering, the snout projects, and the mouth is placed ventrally some distance from the end of the snout. There are two dorsal fins, each of which is armed on its anterior edge with a sharp and slightly curved spine, hence its name "picked." This species is viviparous, the female producing five to nine young at a birth; the young when born are 9 to 10 in. long and quite similar to the parents in all respects except size. It is gregarious, and is abundant at all seasons everywhere on the British coasts. In 1858 an enormous shoal of dog-fish, many square miles in extent, appeared in the north of Scotland, when, says J. Couch, "they were to be found floating in myriads on the surface of every harbour." They are the special enemies of the fisherman, injuring his nets, removing the hooks from his lines, and spoiling his fish for the market by biting pieces out of them as they hang on his lines. They are however eaten, both fresh and salted, by fishermen, especially on the west coast of England, and they are sold regularly in the French markets.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)