tuna or tunny, game and food fishes, the largest members of the family Scombridae (mackerel family) and closely related to the albacore and bonito. They have streamlined bodies with two fins, and five or more finlets on the back. The body is very narrow in the tail region, and the tail is deeply forked.

The most important commercially of the group called little tunnies is the little tuna, or false albacore, Euthynnus alleteraturs, which averages 10 lb (4.5 kg) and is found in open Atlantic waters north to Cape Cod. The oceanic bonito, or skipjack, Katsuwonus pelamis, is a warm-water fish reaching 20 lb (9 kg) in weight. The albacore, or long-finned tuna, Thunnus alalunga (up to 60 lb/27 kg), is found in tropical and temperate ocean waters (including the Mediterranean); its flesh is marketed as “whitemeat tuna.” The Atlantic bluefin tuna, T. thynnus, the largest of the great tunnies and the giant of bony fishes, averages 200 to 500 lb (90–225 kg) with adults sometimes reaching 14 ft (427 cm) and 3⁄4 tons (680 kg). The Pacific bluefin tuna, T. orientalis, of similar size, and the Altantic are sometimes treated as subspecies of the northern bluefin; both are found in the Northern Hemisphere. The southern bluefin, of the same genus but a little smaller, is found in the Southern Hemisphere. Bluefin are highly prized as sport fishes as well as by commerce. The yellowfin tuna, T. albacares, is smaller (125 lb/56 kg) and found in tropical and subtropical open ocean waters worldwide.

Tuna fisheries have been important commercially in Europe for centuries and are the backbone of a major canning industry on both coasts of North America. Tuna fishing is controlled by international agreements, but catch limits and other regulations have not been adhered to. As a result, some tuna fisheries have been overfished, and the albacore, bluefin, yellowfin, and other species are considered threatened. Another major marine conservation problem has been the use of huge drift nets to capture tuna, because the nets also trap and kill thousands of seals, dolphins, whales, and sea birds in the process. Although nets longer than 1.5 mi (2.4 km) have been banned worldwide, nets up to 20 mi (32 km) are still commonly used in defiance of the ban in parts of the world.

Tunas are classified in the phylum Chordata, subphylum Vertebrata, class Actinopterygii, order Perciformes, family Scombridae.

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