The spiny dogfish, spurdog, or piked dogfish, Squalus acanthias, is one of the best known of the dogfish, members of the family Squalidae in the order Squaliformes. While these common names may apply to several species, Squalus acanthias is readily distinguished by having two spines (one anterior to each dorsal fin) and its lack of an anal fin. It is found in shallow waters and offshore in most parts of the world, especially in temperate waters.

Morphology and behavior

The spiny dogfish has dorsal spines, no anal fin, and white spots along its back. The caudal fin has asymmetrical lobes, forming a heterocercal tail. Males mature at around 11 years of age, growing to 80-100 cm in length; females mature in 18-21 years and are slightly larger than males, reaching 98.5-159 cm (3.25 to 5.25 ft). Both sexes are greyish brown in color and are countershaded. Males are identified by a pair of pelvic fins modified as sperm-transfer organs, or "claspers". The male inserts one clasper into the female cloaca during copulation.

The species name acanthias refers to the shark's two spines. These are used defensively; if captured, the shark can arch its back to pierce its captor. Glands at the base of the spines secrete a mild poison.

Reproduction is aplacental viviparous, which was before called ovoviviparity. Fertilization is internal. The male inserts one clasper into the female oviduct orifice and injects sperm along a groove on the clasper's dorsal section. Immediately following fertilization, the eggs are surrounded by thin shells called candles, with one candle usually surrounding several eggs. Mating takes place in the winter months, with gestation lasting 22-24 months (the longest of any vertebrate). Litters range between 2 and 11 but average 6 or 7.

Commercial use

Spiny dogfish are fished for food in Europe, the United States, Canada, New Zealand and Chile. The meat is primarily consumed in England, France, the Benelux countries and Germany. The fins and tails are processed into fin needles and are used in less expensive versions of shark fin soup in Chinese cuisine. In England it is sold in "fish and chip shops" as "rock salmon", in France it is sold as "small salmon" (saumonette) and in Belgium it is sold as "sea eel" (zeepaling). It is also used as fertilizer, liver oil, and pet food, and, because of its availability and manageable size, as a popular vertebrate dissection specimen, especially in high schools.

See also

• List of sharks

References

• Database entry includes a lengthy justification of why this species is vulnerable

External links

• Spiny dogfish attacked by North Pacific Giant Octopus
• Spiny dogfish at Animal Diversity Web