Spiny dogfish

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Spiny dogfish

Conservation status

Vulnerable

Scientific classification

Kingdom:	Animalia
Phylum:	Chordata
Class:	Chondrichthyes
Subclass:	Elasmobranchii
Order:	Squaliformes
Family:	Squalidae
Genus:	Squalus
Species:	S. acanthias

Binomial name

Squalus acanthias
Linnaeus, 1758

Sharks Portal

The spiny dogfish or piked dogfish, Squalus acanthias, is one of the best known of the dogfish, members of the family Squalidae in the order Squaliformes. There are actually several species to which the names are applied, but all are readily distinguished by their having two spines (one anterior to each dorsal fin) and their lack of an anal fin. It is found in shallow waters and offshore in most parts of the world, especially in temperate waters.

1 Morphology and behavior
2 Commercial use
3 See also
4 References
5 External links

[edit] 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 100-124 cm. 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.

The spiny dogfish forms large schools of hundreds to thousands of sharks. It is from this behavior that their name is derived, as fisherman likened these large schools to packs of dogs. Schools are often composed entirely of sharks of like size and sex. The shark feeds on bony fishes, smaller sharks, and various invertebrates. It is also a common prey item for large fish, other sharks, and marine mammals.

Reproduction is aplacental viviparous, which was before called ovoviviparity. Fertilization is internal. The male inserts one claspers 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.

[edit] 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.