The blue shark (Prionace glauca) is a species of requiem shark, family Carcharhinidae, that inhabits deep waters in the world's temperate and tropical oceans. Preferring cooler waters, blue sharks migrate long distances, for example from New England to South America. Although generally lethargic, they can move very quickly. Blue sharks are viviparous and are noted for large litters of 25 to over 100 pups. They feed primarily on small fish and squid, although they can take larger prey. Blue sharks often school segregated by sex and size, and this behavior has led to their nickname 'wolves of the sea'. Blue sharks are light-bodied with long pectoral fins. The top of the body is deep blue, lighter on the sides, and the underside is white. It grows to 3.8 meters (12.5 ft) long and can weigh up to 204 kilograms (450 lb). The heaviest reported weight was 391 kilograms (860 lb) . They are viviparous, with a yolk-sac placenta, delivering 4 to 135 pups per litter.