44 BULLETIN OF THE BUREAU OF FISHERIES 



THE SPINY DOGFISHES. FAMILY SQUALID^ 



This group is characterized and made easily recognizable by the presence of 

 two dorsal fins, each with a fixed spine, but no anal fin, while the teeth are alike in 

 the two jaws in some, unlike in others. 



15. Spiny dogfish (Squalus acanthias Linnaeus) 



Dogfish; Piked dogfish; Grayfish 



Jordan and Evermann, 1896-1900, p. 54. 

 Garman, 1913, p. 192. 



Description. — So rare are all other spiny sharks in the Gulf of Maine that any 

 little shark with a large sharp spine close in front of each dorsal fin caught there is 

 practically sure to be a "dog," of which there are thousands in the Gulf to one 

 of any other shark. Should the fish be uniform dark brown or black it might 

 possibly (but not probably) prove to be the black dogfish (p. 52). A glance at the 

 tail fin will settle the question, for the rear margin of the latter is deeply notched 

 near its tip (fig. 19), whereas in the common spiny dog its margin is entire. 



This is a slender little shark with tapering but rounded head and flattened snout. 

 Its first dorsal fin stands between pectoral and ventral; its second dorsal is about 



Fig. 16. — Spiny dogfish (Squalia acanthias). After Garman 



two-thirds as large as the first; its pectoral is triangular, broader at the base than it is 

 long; the lower lobe of the tail fin is well marked; and the ventrals are well forward 

 of the second dorsal. The spines are close up against the front margins of the two 

 dorsals, the first shorter and the second nearly as long as their respective fins are 

 high, and they are very sharp, as every fisherman knows to his cost. The spiny dog 

 has no anal fin, a lack separating it from all smooth-finned sharks known from the 

 Gulf of Maine, except the Greenland shark (p. 53). There is a low fold of skin on 

 either side of the root of the tail back of the second dorsal fin, so small, however, 

 that there is no danger of confusing it with the keels of the mackerel sharks. The 

 teeth are small, their sharp points bent toward the outer corners of the mouth and 

 each row forming a continuous cutting edge. 



Size. — Mature dogs are ordinarily 2 to 3}4 feet long. Mature males grow to a 

 length of about 3 feet and a weight of 5 to 6 pounds; females to 3 or 3J^ feet and a 

 weight of 8 pounds. Occasionally very large fat specimens may reach a weight of 

 15 pounds. 



