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Tuna, sometimes called tunafish, are several species of ocean-dwelling fish in the family Scombridae, mostly in the genus Thunnus.


 


Speed racer: Tuna are fast swimmers (they have been measured at 77 km/h (48 mph)) and include several species that are warm-blooded. Unlike most fish species, which have white flesh, the flesh of tuna is pink to dark red. This is because tuna muscle tissue contains greater quantities of myoglobin, an oxygen-binding molecule, than the muscle tissue of most other fish species. Some of the larger tuna species such as the bluefin tuna can raise their blood temperature above the water temperature with muscular activity. This enables them to live in cooler waters and survive a wider range of circumstances.

Tuna Business: Tuna is an important commercial fish. Some varieties of tuna, such as the bluefin and bigeye tuna are threatened by overfishing, dramatically affecting tuna populations in the Atlantic and northwestern Pacific Oceans. Other populations seem to support fairly healthy fisheries (for example, the central and western Pacific skipjack tuna), but there is mounting evidence that overcapitalization threatens tuna fisheries world-wide.

Increasing quantities of high-grade tuna are entering the market from operations that rear tuna in net pens and feeding them on a variety of bait fish. In Australia the Southern Bluefin tuna is one of two species of bluefin tunas that is kept in tuna farms by former fishermen. Its close relative, the Northern Bluefin Tuna, is being used to develop tuna farming industries in the Mediterranean, North America and Japan.

Health Watch: Due to their high position in the food chain and the subsequent accumulation of heavy metals from their diet, mercury levels can be relatively high in some of the larger species of tuna such as bluefin and albacore. As a result, in March 2004 the United States FDA issued guidelines recommending pregnant women, nursing mothers and children to limit their intake of tuna and other types of predatory fish. However, most canned light tuna is skipjack tuna and is very low in mercury.

Tuna are a common target for big-game fishing, and are mostly caught on artificial lures.

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 Kingdom: Animalia

 Phylum: Chordata

 Class: Actinopterygii

 Order: Perciformes

 Family: Scombridae

 Genus: Thunnus