Tuna are several species of ocean-dwelling fish in the family Scombridae, mostly in the genus Thunnus. Tuna are fast swimmers 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 is a popular seafood. Some varieties of tuna, such as the bluefin and Bigeye tuna are threatened by overfishing, dramatically affecting tuna populations in the Atlantic and north western Pacific Oceans. Other populations seem to support fairly healthy fisheries (e.g. central and western Pacific skipjack), 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.

Due to their higher 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 fish 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 tunafish and other types of predatory fish. Most canned light tuna is the skipjack of light tuna and is very low in mercury.

Fish Recipes

• Bluefin tuna, which can grow to 1,500 lb (680 kg)
• Yellowfin tuna
• Albacore tuna
• Bigeye tuna
• Blackfin tuna

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

Top speed

Tuna have been measured swimming at 77 kilometers per hour (47.85 MPH).

Tuna farming

In Australia the southern bluefin tuna fish is one of two species of bluefin tunas that is kept in tuna farms by former fishermen. Its close relative, the northern bluefin tunafish, is being used to develop tuna fish farming industries in the Mediterranean, North America and Japan.

Other species

Species of several other genera (all in Scombridae) are commonly named "tunafish":

• Skipjack tunafish Katsuwonus pelamis
• Slender tunafish Allothunnus fallai
• Bullet tunafish Auxis rochei rochei
• Frigate tunafish Auxis thazard thazard
• Kawakawa (little tunafish or mackerel tunafish) Euthynnus affinis
• Little tunny (little tunafish) Euthynnus alletteratus
• Butterfly kingfish (Butterfly tunafish) Gasterochisma melampus
• Dogtooth tunafish Gymnosarda unicolor