swordfish, large food and game fish, Xiphias gladius, of the warmer Atlantic and Pacific waters, related to the sailfish. It is named for its sharp, broad, elongated upper jaw, which it uses to flail and pierce its prey of smaller fish, rising beneath a school to kill and then devour. Swordfish breed as far N as Nova Scotia; they are often seen basking on the water's surface, and their fins are sometimes mistaken for those of sharks. They may reach 15 ft (457 cm) and 1,000 lb (450 kg); however, specimens half this size are considered large. Swordfish were formerly harpooned commercially but now are taken using long lines with multiple baited hooks. Conservation efforts are underway to rebuild depleted stocks. Swordfish are classified in the phylum Chordata, subphylum Vertebrata, class Osteichthyes, order Perciformes, family Xiphiidae.