A tuna (: tunas or tuna) is a saltwater fish that belongs to the tribe Thunnini, a subgrouping of the Scombridae (mackerel) family. The Thunnini comprise 15 species across five genera,[ the sizes of which vary greatly, ranging from the bullet tuna (max length: , weight: ) up to the Atlantic bluefin tuna (max length: , weight: ), which averages and is believed to live up to 50 years.
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Tuna, opah, and are the only species of fish that can mesotherm. An active and agile predator, the tuna has a sleek, streamlined body, and is among the fastest-swimming pelagic fish—the yellowfin tuna, for example, is capable of speeds of up to .
Found in warm seas, the tuna is commercially fished extensively as a food fish, and is popular as a blue water game fish. As a result of overfishing, some tuna species, such as the southern bluefin tuna, are threatened with extinction.
Etymology
The term "tuna" comes from Spanish language atún < Andalusian Arabic at-tūn, assimilated from al-tūn التون Modern : 'tuna fish' < Middle Latin thunnus.[.]
In English, tuna has been referred to as Chicken of the Sea. This name persists today in Japan, where tuna as a food can be called shi-chikin, literally "sea chicken".
Taxonomy
The Thunnini tribe is a monophyletic clade comprising 15 species in five genera:
- * family Scombridae
- ** tribe Thunnini: tunas
- *** genus Allothunnus: slender tunas
- *** genus Auxis: frigate tunas
- *** genus Euthynnus: little tunas
- *** genus Katsuwonus: skipjack tunas
- *** genus Thunnus: albacores and true tunas
- **** subgenus Thunnus (Thunnus): bluefin group
- **** subgenus Thunnus (Neothunnus): yellowfin group
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. The following cladogram illustrates the relationship between the tunas and other tribes of the family Scombridae. For example, the cladogram illustrates that the are more closely related to the than are the (the most primitive of the tunas), and that the next nearest relatives of the tunas are the of the tribe Sardini.[
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True species
The "true" tunas are those that belong to the genus Thunnus. Until recently, it was thought that there were seven Thunnus species, and that Atlantic bluefin tuna and Pacific bluefin tuna were subspecies of a single species. In 1999, Collette established that based on both molecular and morphological considerations, they are in fact distinct species.
The genus Thunnus is further classified into two subgenera: Thunnus (Thunnus) (the bluefin group), and Thunnus (Neothunnus) (the yellowfin group).
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Other species
The Thunnini tribe also includes seven additional species of tuna across four genera. They are:
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Biology
Description
The tuna is a sleek, elongated and streamlined fish, adapted for speed. It has two closely spaced but separated dorsal fins on its back; The first fin is "depressible" – it can be laid down, flush, in a groove that runs along its back; it is supported by spines.
The tuna's body is countershading to camouflage itself in deeper water when seen from above, its dorsal side is generally a metallic dark blue while the ventral or under side is silvery, often with an Iridescence shine.[ The caudal peduncle, to which the tail is attached, is quite thin, with three stabilizing horizontal Homocercal on each side.][
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Physiology
Thunnus are widely but sparsely distributed throughout the oceans of the world, generally in tropical and temperate waters at ranging between about 45° north and south of the equator.
Tunas achieve endothermy by conserving the heat generated through normal metabolism. In all tunas, the heart operates at ambient temperature, as it receives cooled blood, and coronary circulation is directly from the gills.[ The rete mirabile ("wonderful net"), the intertwining of veins and arteries in the body's periphery, allows nearly all of the metabolic heat from venous blood to be "re-claimed" and transferred to the arterial blood via a counter-current exchange system, thus mitigating the effects of surface cooling.]
Also unlike most fish, which have white flesh, the muscle tissue of tuna ranges from pink to dark red. The red Myotome muscles derive their color from myoglobin, an oxygen-binding molecule, which tuna express in quantities far higher than most other fish. The oxygen-rich blood further enables energy delivery to their muscles.[
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For powerful swimming animals like and tuna, cavitation may be detrimental, because it limits their maximum swimming speed.[
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Fishing
Commerce
Tuna is an important commercial 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).
Based on catches from 2007, the report states:
The Australian government alleged in 2006 that Japan had illegally overfished southern bluefin by taking 12,000 to 20,000 tonnes per year instead of the agreed upon 6,000 tonnes; the value of such overfishing would be as much as US$2 billion.
In recent years, opening day fish auctions at Tokyo's Tsukiji fish market and Toyosu Market have seen record-setting prices for bluefin tuna, reflecting market demand. In each of 2010, 2011, 2012, 2013 and 2019, new record prices have been set for a single fish – the current record is 333.6 million japanese yen (US$3.1 million) for a bluefin, or a unit price of JP¥ 1,200,000/kg (US$5,057/lb). The opening auction price for 2014 plummeted to less than 5% of the previous year's price, which had drawn complaints for climbing "way out of line".
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| 2001 | | ¥20.2 million | $173,600 | ¥100,000 / kg | $386 / lb | |
| 2010 | | ¥16.28 million | $175,000 | ¥70,172 / kg | $343 / lb | |
| 2011 | | ¥32.49 million | $396,000 | ¥95,000 / kg | $528 / lb | |
| 2012 | | ¥56.49 million | $736,000 | ¥210,000 / kg | $1,247 / lb | |
| 2013 | | ¥155.4 million | $1.76 million | ¥703,167 / kg | $3,603 / lb | |
| 2019 | | ¥333.6 million | $3.1 million | ¥1,200,000 / kg | $5,057 / lb | |
In November 2011, a different record was set when a fisherman in Massachusetts caught an tuna. It was captured inadvertently using a dragnet. Due to the laws and restrictions on tuna fishing in the United States, federal authorities impounded the fish because it was not caught with a rod and reel. Because of the tuna's deteriorated condition as a result of the trawl net, the fish sold for just under $5,000.
File:TunaFish.JPG|Tuna being weighed on Greek quay-side
File:Tsukiji Fish market and Tuna edit.jpg|Tuna at Tsukiji fish market, Tokyo
File:Tuna cut half japan.jpg|Tuna cut in half for processing at Tsukuji fish market
Methods
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.
Association with whaling
In 2005, Nauru, defending its vote from Australian criticism at that year's meeting of the International Whaling Commission, argued that some whale species have the potential to devastate Nauru's tuna stocks, and that Nauru's food security and economy relies heavily on fishing.
Association with dolphins
swim beside several tuna species. These include yellowfin tuna in the eastern Pacific Ocean, but not albacore. Tuna schools are believed to associate themselves with dolphins for protection against sharks, which are tuna .
Commercial fishing vessels used to exploit this association by searching for dolphin pods. Vessels would encircle the pod with nets to catch the tuna beneath.
Fishery practices have changed to be dolphin friendly, which has caused greater bycatch including , 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. Measures taken thus far to satisfy the public demand to protect dolphins can be potentially damaging to other species as well.
Aquaculture
Increasing quantities of high-grade tuna caught at sea are reared in net pens and fed bait fish. In Australia, former fishermen raise southern bluefin tuna ( Thunnus maccoyii) and another bluefin species.[
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Japan is the biggest tuna consuming nation and is also the leader in tuna farming research.[
] Japan first successfully farm-hatched and raised bluefin tuna in 1979. In 2002, it succeeded in completing the reproduction cycle and in 2007, completed a third generation.[
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Food
Fresh and frozen
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. When served as a steak, the meat of most species is known for its thickness and firm texture. In the U.K., supermarkets began flying in fresh tuna steaks in the late 1990s, which helped to increase the popularity of using fresh tuna in cooking; by 2009, celebrity chefs regularly featured fresh tuna in salads, wraps, and char-grilled dishes.
Served raw
Various species of tuna are often served raw in Japanese cuisine as sushi or sashimi.
Commercial sashimi tuna may have their coloration fixated by pumping carbon monoxide (CO) into bags containing the tuna, and holding it at 4°C. For a 2-inch tuna steak, this requires 24 hours. The fish is then vacuum sealed and frozen. In Japan, color fixation using CO is prohibited.
Tuna consumption increases the risk of getting cancer.
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Canned
Tuna is canned in edible Vegetable oil, in brine, in water, and in various sauces. Tuna may be processed and labeled as "solid", "chunked" ("chunk") or "flaked". When tuna is canned and packaged for sale, the product is sometimes called tuna fish (U.S.), a calque (loan translation) from the German language . Canned tuna is sometimes used as food for pets, especially .
- Australia
Canned fish tuna was first produced in Australia in 1903 and quickly became popular.[ Choice: Jan/Feb 2004.]
In the early 1980s canned tuna in Australia was most likely southern bluefin, it was usually yellowfin, Skipjack tuna, or tongol (labelled "northern bluefin" or "longtail").
Australian standards once required cans of tuna to contain at least 51% tuna, but those regulations were dropped in 2003.[ Choice, August 2003.][ Test: Canned tuna (archived) Canned or conned? ] The remaining weight is usually oil or water.
- United States
The product became more plentiful in the United States in the late 1940s. In 1950, 8,500,000 pounds of canned tuna were produced, and the U.S. Department of Agriculture classified it as a "plentiful food".
In the United States, 52% of canned tuna is used for Tuna sandwich; 22% for ; and 15% for and dried, prepackaged , such as General Mills's Hamburger Helper line.["Tuna". Modern Marvels, 4 February 2010.] Other canned tuna dishes include (a type of sandwich where the tuna is mixed with mayonnaise and served on bread with cheese melted on top); salade niçoise (a salad made of tuna, olives, green beans, potatoes, hard-boiled eggs and anchovy dressing); and tuna burgers (served on buns).
In the United States, the Food and Drug Administration (FDA) regulates canned tuna (see part c).
- Precooked
As tunas are often caught far from where they are processed, poor interim conservation can lead to spoilage. Tuna is typically gutted by hand, and later precooked for prescribed times of 45 minutes to three hours. The fish are then cleaned and Fish fillet, canned (and sealed), with the dark lateral blood meat often separately canned for pet food (Cat food or Dog food). The sealed can is then heated under pressure (called "Pressure cooking") for 2–4 hours.
- Light and white
In some markets, depending upon the color of the flesh of the tuna species, the can is marked as "light" or "white" meat, with "light" meaning a greyish pink color and "white" meaning a light pink color. In the United States, only albacore can legally be sold in canned form as "white meat tuna";[Ellis, Richard. Tuna: A Love Story. New York: Random House, 2009, p. 119. ] in other countries, Yellowfin tuna is also acceptable.
- Ventresca tuna
Ventresca tuna (from ventre, the Italian word for belly),
Nutrition
Canned light tuna in oil is 29% protein, 8% fat, 60% water, and contains no , while providing 200 in a 100 gram reference amount (table). It is a rich source (20% or more of the Daily Value, DV) of phosphorus (44% DV) and vitamin D (45% DV), and a moderate source of iron (11% DV).
Mercury and health
Mercury content in tuna can vary widely. 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.
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.
A January 2008 report revealed potentially dangerous levels of mercury in certain varieties of sushi tuna, reporting levels "so high that the Food and Drug Administration could take legal action to remove the fish from the market."
Management and conservation
The main tuna fishery management bodies are the Western and Central Pacific Fisheries Commission, the Inter-American Tropical Tuna Commission, the Indian Ocean Tuna Commission, the International Commission for the Conservation of Atlantic Tunas, and the Commission for the Conservation of Southern Bluefin Tuna.
In 2010, Greenpeace International added the albacore, bigeye tuna, Pacific bluefin tuna, Atlantic bluefin tuna, southern bluefin tuna, and yellowfin tuna to its seafood red list, which are fish "commonly sold in supermarkets around the world, and which have a very high risk of being sourced from unsustainable fisheries."
Bluefin tuna have been widely accepted as being severely Overfishing, with some stocks at risk of collapse.[Ito, Masami, " Does Japan's affair with tuna mean loving it to extinction?", Japan Times, 31 August 2010, p. 3. ] According to the International Seafood Sustainability Foundation (a global, nonprofit partnership between the tuna industry, scientists, and the World Wide Fund for Nature), Indian Ocean yellowfin tuna, Pacific Ocean (eastern and western) bigeye tuna, and North Atlantic albacore tuna are all overfished. In April 2009, no stock of skipjack tuna (which makes up roughly 60% of all tuna fished worldwide) was considered to be overfished.
The BBC documentary South Pacific, which first aired in May 2009, stated that, should fishing in the Pacific continue at its current rate, populations of all tuna species could collapse within five years. It highlighted huge Japanese and European tuna fishing vessels, sent to the South Pacific international waters after overfishing their own fish stocks to the point of collapse.
A 2010 tuna fishery assessment report, released in January 2012 by the Secretariat of the Pacific Community, supported this finding, recommending that all tuna fishing should be reduced or limited to current levels and that limits on skipjack fishing be considered.
Research
See also
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Environmental impact of fishing
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Got Mercury?
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List of tuna dishes
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Natal homing
Further references
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Clover, Charles. 2004. . Ebury Press, London.
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FAO: Species Catalog Vol. 2 Scombrids of the World. FAO Fisheries Synopsis No. 125, Volume 2. FIR/S125 Vol. 2.
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FAO: Review of the state of world marine fishery resources: Tuna and tuna-like species – Global, 2005 Rome.
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Majkowski, Jacek (1995) "Tuna and tuna-like species" In: Review of the state of world marine fishery resources, FAO Fisheries technical paper 457, FAO, Rome. .
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Majkowski J, Arrizabalaga H, Carocci F and Murua H (2011) "Tuna and tuna-like species" In: Review of the state of world marine fishery resources, pages 227–244, FAO Fisheries technical paper 569, FAO, Rome. .
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Standard of Identity for Canned Tuna (United States), Code of Federal Regulations: 21 CFR 161.190 – Canned tuna.
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Viñas J and Tudela S (2009) "A validated methodology for genetic identification of tuna species (genus Thunnus)" PLoS One, 4(10): e7606.
Further reading
