Any of several species of small
The spiny dogfish ( Squalus acanthias , family Squalidae) has a sharp spine in front of each of its two dorsal fins. It is abundant along northern Atlantic and Pacific coasts. It is gray with white spots, about 2–4 ft (60–120 cm) long, and often found in schools. It preys on fishes and invertebrates and often steals bait and damages fishing nets. It yields liver oil or is ground for fertilizer. Other well-known species are the spotted dogfishes (family Scyliorhinidae), which are sold as food, and the smooth hound or smooth dogfish ( Mustelus canis , family Triakidae), one of the most common sharks on the U.S. Atlantic coast. See also {{link=bowfin">bowfin .