CHARACTERISTICS OF VALUABLE MARINE FISHES 41 



certain districts eaten as food or salted for use as bait. One of 

 the commonest is the spiny dog-fish, often called the spur-dog, 

 or picked dog-fish (Fig. 4). It has a strong sharp spine in front 

 of each of the two dorsal fins, and has no ventral fin. It is a 

 strong active swimmer which roams about in shoals pursuing and 

 preying upon smaller bony fishes such as herring and pilchard. 

 It is often very troublesome to drift-net fishermen on account 

 of the damage it does to their nets. The Greenland shark, 

 which has been frequently taken off our more northern coasts, 

 resembles the spur-dog in having no ventral fin, but it has no 

 spines connected with the dorsal fins. Its usual length is from 

 eleven to fourteen feet. The spotted dog-fishes are very com- 

 mon, and as they live on and near the bottom are usually taken 

 in the trawl. There are two kinds, the larger with large spots, 

 the smaller with more numerous small spots. In these species 



FIG. 4. The Spiny Dog-fish, or Spur-dog. 



the two dorsal fins are placed far back and rather close together, 

 the ventral fin being opposite to the interval between them. 

 The teeth are small, numerous, and pointed. 



Two other common dog-fishes are the tope and the smooth- 

 hound. They belong to the same family, in the members of 

 which the dorsal fins are far apart, and the ventral is opposite 

 the second dorsal. In the tope the teeth are large and sharp, 

 in the smooth-hound they are small and flat or pavement-like. 

 Both are often taken in the trawl, and reach a length of four or 

 five feet. The blue shark is a long slender fish, similar to the 

 dog-fishes just mentioned. It is said to grow to twenty-five 

 feet in length, but only young specimens six or eight feet long 

 are usually taken in British waters. These are not uncommonly 

 caught in drift-nets off the Cornish coasts. 



The porbeagle, the thrasher or fox-shark, and the basking 

 shark, are three kinds of large but comparatively inoffensive 



