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 Pacific albacore, or long-finned tuna, Thunnus alalunga (up to 60 lb/27 kg), is found off the Pacific coast of the United States and in the Mediterranean; its flesh is marketed as whitemeat tuna. The 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 bluefin, also called horse, or jack, mackerel, is cosmopolitan in distribution; in the Atlantic, schools of bluefins travel as far N as Nova Scotia in the spring and summer. It is highly prized as a sports fish as well as by commerce. The yellowfin tuna, T. albacares, is smaller (125 lb/56 kg) and more southerly in range.

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. The tuna fishery is controlled by international agreements, but catch limits and other regulations are not always observed. As a result, some tuna fisheries have been overfished. 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 much of the Mediterranean and parts of the Atlantic.

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