Spiny dogfish

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Spiny dogfish
Conservation status
Vulnerable (VU)
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

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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.

[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 ovoviviparous. 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.

[edit] See also

• List of sharks

[edit] References

• Fordham et al (2006). Squalus acanthias. 2006 IUCN Red List of Threatened Species. IUCN 2006. Retrieved on 11 May 2006. Database entry includes a lengthy justification of why this species is vulnerable
• Squalus acanthias (TSN 160617). Integrated Taxonomic Information System. Accessed on 24 January 2006.
• "Squalus acanthias". FishBase. Ed. Ranier Froese and Daniel Pauly. 10 2005 version. N.p.: FishBase, 2005.

[edit] External links

• Spiny dogfish attacked by North Pacific Giant Octopus