DOG-FISH, the popular name of several species of small shark (q.v.), chiefly belonging to Mustelus and Squalus, two quite unlike genera. The name is derived from their habit of swimming in schools or packs in pursuit of their food. In their general anatomy, they differ but little from the other sharks, so well known for their ferocious habits. The dog fishes, though among the smallest of the tribe, manifest propensities equally cruel with those which have rendered the white shark and others so justly dreaded. Although seldom or never injurious to man, they commit great ravages in the fisheries, and where they abound constitute one of the greatest nuisances to the fishermen. Exceedingly voracious, and devouring almost everything which they en counter, the mischief they occasion by taking the baits, and very often the hooks, of the deep-sea lines, is very considerable and not at all compensated for by the flesh of those which are captured.
The smooth dog-fish or dog-shark (M. cans) is found on both sides of the north Atlantic, and on the American side is particularly abundant south of Cape Cod. It is from two to three feet long. No spines occur in the margins of the dorsal fins, and the smooth pavement-like teeth are especially adapted for crushing crabs, lobsters and other testaceous invertebrates on which they chiefly feed. The young are hatched from the egg in the oviducts of the female (with which, however, they are not connected by a placenta, as in the related Galescs nsustelus of Europe), and are born alive. The eggs are similar to others of the family and covered by a tough membranaceous integument. The skin
of these fish is beset with numerous small as perities, which render it, when dried, well adapted for polishing wood and for other mechanical purposes.
The spiny dog-fish (Squalus aranthias) is very abundant on the coasts of New England, and, although similar in size and general aspect, is readily distinguished from the smooth dog fish by the presence of a strong spine before each of the two dorsal fins. The eggs are de posited before hatching. This species furnishes material for a valuable fishery and fish industry in Maine, where the oil is extracted from the livers, the flesh ground up for fertilizers or poultry food and the skin utilized for polishing metal and wood. The dog-fish feeds chiefly on herring and mackerel, the schools of which it follows in immense numbers. Similar species occur in the Pacific Ocean and other seas.
The flesh of all the species is hard, dry and npalatable, requiring to be well soaked before it is eaten. In England the dried flesh goes under the name of Folkestone beef. Poisonous effects are at certain times observed in conse quence of eating the livers of dog-fish and some cases are recorded in which the most distressing illness has been by the practice. The name dog-fish is also applied to several other quite distinct fishes, more particularly to the western mud-fish or bow-fin (Amia calm), and to the dog-salmon (Oncorhynchus keta).