Tuna, opah, and mackerel sharks are the only species of fish that can maintain a body temperature higher than that of the surrounding water.

This name persists today in Japan, where tuna as a food can be called シーチキン (shi-chikin), literally "sea chicken".

The Thunnini tribe is a monophyletic clade comprising 15 species in five genera: The cladogram is a tool for visualizing and comparing the evolutionary relationships between taxa, and is read left-to-right as if on a timeline.

[42] Seven to ten yellow finlets run from the dorsal fins to the tail, which is lunate – curved like a crescent moon – and tapered to pointy tips.

[43] Thunnus are widely but sparsely distributed throughout the oceans of the world, generally in tropical and temperate waters at latitudes ranging between about 45° north and south of the equator.

In all tunas, the heart operates at ambient temperature, as it receives cooled blood, and coronary circulation is directly from the gills.

[48] This allows the tuna to elevate the temperatures of the highly-aerobic tissues of the skeletal muscles, eyes and brain,[46][47] which supports faster swimming speeds and reduced energy expenditure, and which enables them to survive in cooler waters over a wider range of ocean environments than those of other fish.

[citation needed] Also unlike most fish, which have white flesh, the muscle tissue of tuna ranges from pink to dark red.

The red myotomal muscles derive their color from myoglobin, an oxygen-binding molecule, which tuna express in quantities far higher than most other fish.

The International Seafood Sustainability Foundation (ISSF) compiled a detailed scientific report on the state of global tuna stocks in 2009, which includes regular updates.

According to the ISSF, the most important species for commercial and recreational tuna fisheries are yellowfin (Thunnus albacares), bigeye (T. obesus), bluefin (T. thynnus, T. orientalis, and T. macoyii), albacore (T. alalunga), and skipjack (Katsuwonus pelamis).

[51] According to the WWF, "Japan's huge appetite for tuna will take the most sought-after stocks to the brink of commercial extinction unless fisheries agree on more rigid quotas".

[60] Besides for edible purposes, many tuna species are caught frequently as game, often for recreation or for contests in which money is awarded based on weight.

Larger specimens are notorious for putting up a fight while hooked, and have been known to injure people who try to catch them, as well as damage their equipment.

[62] Despite this, Nauru does not permit whaling in its own waters and does not allow other fishing vessels to take or intentionally interact with marine mammals in its Exclusive Economic Zone.

Public outcry and new government regulations, which are now monitored by NOAA have led to more dolphin-friendly methods, now generally involving lines rather than nets.

Fishery practices have changed to be dolphin friendly, which has caused greater bycatch including sharks, turtles and other oceanic fish.

Fishermen no longer follow dolphins, but concentrate their fisheries around floating objects such as fish aggregation devices, also known as FADs, which attract large populations of other organisms.

[66] Increasing quantities of high-grade tuna caught at sea are reared in net pens and fed bait fish.

[61] Farming its close relative, the Atlantic bluefin tuna, Thunnus thynnus, is beginning in the Mediterranean, North America and Japan.

[72] In 2009, Clean Seas, an Australian company which has been receiving assistance from Kinki University[73][74][75] managed to breed southern bluefin tuna in captivity and was awarded the second place in World's Best Invention of 2009 by Time magazine.

[76][77] The fresh or frozen flesh of tuna is widely regarded as a delicacy in most areas where it is shipped, being prepared in a variety of ways.

An Australian study of 53 varieties of unflavored canned tuna found none to exceed the safe histamine level, although some had "off" flavors.

[90][91] Canned light tuna in oil is 29% protein, 8% fat, 60% water, and contains no carbohydrates, while providing 200 calories in a 100 gram reference amount (table).

Among those calling for improved warnings about mercury in tuna is the American Medical Association, which adopted a policy that physicians should help make their patients more aware of the potential risks.

[94] A study published in 2008 found that mercury distribution in the meat of farmed tuna is inversely related to the lipid content, suggesting that higher lipid concentration within edible tissues of tuna raised in captivity might, other factors remaining equal, have a diluting effect on mercury content.

[97] In March 2004, the United States FDA issued guidelines recommending that pregnant women, nursing mothers, and children limit their intake of tuna and other predatory fish.

[101] In 2009, a California appeals court upheld a ruling that canned tuna does not need warning labels as the methylmercury is naturally occurring.

The bigeye tuna catch rates have also declined abruptly during the past half century, mostly due to increased industrial fisheries, with the ocean warming adding further stress to the fish species.