Squalus acanthias

The spiny dogfish, spurdog, mud shark, or piked dogfish (Squalus acanthias) is one of the best known species of the Squalidae (dogfish) family of sharks, which is part of the Squaliformes order. While these common names may apply to several species, Squalus acanthias is distinguished by having two spines (one anterior to each dorsal fin) and lacks an anal fin. It is found mostly in shallow waters and further offshore in most parts of the world, especially in temperate waters. Spiny dogfish in the northern Pacific Ocean have recently been reevaluated and found to constitute a separate species, now known as 'Pacific spiny dogfish', Squalus suckleyi. The spiny dogfish has dorsal fins, no anal fin, and dark green spots along its back. The caudal fin has asymmetrical lobes, forming a heterocercal tail.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 with spines near the dorsal fins that secrete a mild venom into its predator. This shark is known to hunt in packs that can range up into the thousands. They are aggressive hunters and have a sizable diet that can range from squid, fish, crab, jellyfish, sea cucumber, shrimp and other invertebrates. Males mature at around 11 years of age, growing to 80–100 cm (31–39 in) in length; females mature in 18–21 years and are slightly larger than males, reaching 98.5–159 cm (38.8–62.6 in). 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. 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. Litters range between two and eleven, but average six or seven. Spiny dogfish are bottom-dwellers. They are commonly found at depths of around 50–149 m (160–490 ft), but have been found deeper than 700 m (2,300 ft). Life span is estimated to be up to 100 years and their gestation period is 22 to 24 months, which is thought to be the longest of any vertebrate. Spiny dogfish are consumed as human food in Europe, the United States, Canada, New Zealand and Chile. The meat is primarily consumed in England, France, Italy, 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 this and other dogfish are sold in fish-and-chip shops as 'huss', and it was historically sold as 'rock salmon' until the term was outlawed by consumer legislation. In France it is sold as 'small salmon' (saumonette) and in Belgium and Germany it is sold as 'sea eel' (zeepaling and Seeaal, respectively). It is also used as fertilizer, liver oil, and pet food. Because of its availability, cartilaginous skull, and manageable size, it is a popular vertebrate dissection specimen in both high schools and universities. Reported catches in 2000–2009 varied between 13,800 tonnes (in 2008) and 31,700 tonnes (in 2000).