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Tuna

(or tunny) a group of large and medium-sized oceanic fish which are a food resource of primary importance.

The name tuna, like most general fish names, is not applied in a uniform way and does not always correspond to the scientific classification of these fish. With rare exceptions it is used only of fish in the family Scombridae, and within that family is reserved almost exclusively for members of the two genera Thunnus (all of whose members except one are always called tuna in English) and Euthynnus (where names such as little tunny, thonine, and kawakawa prevail). Within the same subfamily as these are two other genera, whose members are likely to be referred to in scientific works as tuna, but which have other common names and are the subjects of separate entries. These are Katsuwonus (one species only, often just called skipjack rather than skipjack tuna), and Auxis (whose members are usually called frigate mackerel). Close relations, with many of the same characteristics as tuna, include bonito. For a catalogue of all these species see Bruce Collette and Cornelia Nauen (1983).

The principal tuna of the world, with their common names, maximum fork length, distribution, and special characteristics, are as follows (but see also skipjack):

• Thunnus alalunga, longfin tuna or albacore, to 127 cm (50″), worldwide in the Atlantic and Indo-Pacific, has long pectoral fins; has its own entry as there is much to be said about it.
• T. albacares, yellowfin tuna (warning: in French this is albacore, see preceding species), to more than 2 m (c.6.5′), record angling weight 176 kg (c.375 lb), worldwide in tropical and subtropical seas but not in the Mediterranean, dorsal and anal fins and finlets bright yellow.
• T. atlanticus, blackfin tuna, to 1 m (39″), occurring only in the W. Atlantic, from Massachusetts down to Brazil, most commonly taken in the Caribbean region, dorsal and anal fins dusky, the first dorsal fin especially dark.
• T. maccoyii, southern bluefin tuna, to 2.2 m (90″), around the world south of 30 degrees S., the southern member of a trio of similar species, the other two of which come next.
• T. obesus, bigeye tuna, to more than 2 m (c.6.5′), worldwide in tropical and subtropical waters but not in the Mediterranean, has relatively large eyes.
• T. thynnus, northern bluefin tuna, to 3 m (over 9′), record angling weight 679 kg (c.1,493 lb), in the Atlantic and Pacific (at least two subspecies are recognized, one for each ocean), always north of the Equator and as far north as Norway, the largest tuna and the one most familiar to Europeans.
• T. tonggol, longtail tuna, to 130 cm (51″), from the Red Sea to SE Asia and Australia.

Tuna are warm-blooded fish, which are in constant need of oxygen. They can only obtain an adequate supply by swimming continuously at a fair speed (so that oxygen-rich water is incessantly rushing over their gills), and for this purpose they need very powerful muscles. It is this dark muscular meat, so different from the white flesh of most fish, that human beings enjoy eating. Large pieces of tuna may be braised like joints of meat. However, it is more usual to cut steaks which may be grilled (US broiled) or cooked in other ways; or not cooked at all, as when the Japanese eat choice fresh pieces of tuna as sashimi. So great is Japanese enthusiasm for tuna that they and N. Americans between them account for half the total catch, although Europe is now the largest market for canned tuna. See also Tunisia for a good dish which uses canned tuna (see canned foods).

Since Archestratus, tuna have been valued in S. Europe as well as in Japan and the Americas and their cookery may be assessed in Davidson (1979, 1981), although this may be considered in the light of Clover's (2004) estimate of the decline in available stocks and their inability to supply rising demand. One response of the fishing industry has been to ‘farm’ tuna, which means catching infant specimens and fattening them in cages, resulting in a market glut today but probably natural dearth tomorrow.

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