marlin, common name for open-sea fish related to the sailfish and swordfish (family Istiophoridae) and prized by sportsmen. The best known is the blue marlin of the genus Makaira, found in the Gulf Stream as far north as Long Island. It may reach 1,000 lb (454 kg) in weight. The upper jaw of the marlin extends into a long spike with which it clubs the small fish on which it feeds. The striped marlin of the Pacific reaches a weight of 300 to 400 lb (135-180 kg); the paler white marlin of the Atlantic rarely exceeds 100 lb (45 kg). Marlins are classified in the phylum Chordata, subphylum Vertebrata, class Osteichthyes, order Perciformes, family Istiophoridae.

Any of four species (genus Makaira, family Istiophoridae) of deep-blue to blue-green marine fish with a long body, a long dorsal fin, a rounded spear extending from the snout (which it uses to club the fish it feeds on), and usually pale vertical stripes. They are highly prized for sport and food. Species range in weight from about 100 lbs (45 kg) to more than 1,500 lbs (700 kg). The Indo-Pacific black marlin (M. nigicans) has a distinctive, stiff pectoral fin set at an angle.

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