The term billfish is applied to a number of different large, predatory fish characterised by their large size (swordfish can be over 4 metres long) and their long, sword-like bill. Billfish include the sailfish and marlin, which make up the family Istiophoridae, and the swordfish, sole member of the family Xiphiidae. They are important apex predators feeding on a wide variety of smaller fish and cephalopods. While billfish are most common in tropical and subtropical waters, swordfish in particular are sometimes found in temperate waters as well. Billfish are characterized by a long spearlike or swordlike upper jaw or beak that may be used to stun prey during feeding; although this bill has been employed in apparent aggression to spear objects, including boats, it is not deliberately used to spear prey. These species are pelagic, migratory, and found in all oceans.
Billfish are exploited both as food and as game fish. Marlin and sailfish are eaten in many parts of the world, and important sport fisheries target these species, for example off the Atlantic coast of Florida. Because of worries about declining populations, sport fishermen and conservationists now work together to gather information on billfish stocks and implement programs such as catch and release, whereby fish are returned to the sea after they have been caught.
Swordfish are large and have meat that is firm and tasty, and are subject to intense fisheries pressure, and in many places where they were formerly abundant they are now comparatively rare.