Tuna
Overview
 
Tuna is a salt water fish from the family Scombridae
Scombridae
Scombridae is the family of the mackerels, tunas, and bonitos, and thus includes many of the most important and familiar food fishes. The family consists of about 55 species in 15 genera and two subfamilies...

, mostly in the genus Thunnus
Thunnus
Thunnus is a genus of ocean-dwelling fish in the family Scombridae, all of which are tuna, although other tuna species are found in other genera. The name of the genus is the Latinized form of the Greek θύννος, thýnnos, tuna, the word being first mentioned in Homer...

. Tuna are fast swimmers, and some species are capable of speeds of 70 km/h (43.5 mph). Unlike most fish, which have white flesh, the muscle tissue of tuna ranges from pink to dark red. The red coloration derives from myoglobin
Myoglobin
Myoglobin is an iron- and oxygen-binding protein found in the muscle tissue of vertebrates in general and in almost all mammals. It is related to hemoglobin, which is the iron- and oxygen-binding protein in blood, specifically in the red blood cells. The only time myoglobin is found in the...

, an oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

-binding molecule, which tuna express in quantities far higher than most other fish. Some larger tuna species, such as bluefin tuna, display some warm-blooded
Warm-blooded
The term warm-blooded is a colloquial term to describe animal species which have a relatively higher blood temperature, and maintain thermal homeostasis primarily through internal metabolic processes...

 adaptations, and can raise their body temperatures above water temperatures by means of muscular activity.
Encyclopedia
Tuna is a salt water fish from the family Scombridae
Scombridae
Scombridae is the family of the mackerels, tunas, and bonitos, and thus includes many of the most important and familiar food fishes. The family consists of about 55 species in 15 genera and two subfamilies...

, mostly in the genus Thunnus
Thunnus
Thunnus is a genus of ocean-dwelling fish in the family Scombridae, all of which are tuna, although other tuna species are found in other genera. The name of the genus is the Latinized form of the Greek θύννος, thýnnos, tuna, the word being first mentioned in Homer...

. Tuna are fast swimmers, and some species are capable of speeds of 70 km/h (43.5 mph). Unlike most fish, which have white flesh, the muscle tissue of tuna ranges from pink to dark red. The red coloration derives from myoglobin
Myoglobin
Myoglobin is an iron- and oxygen-binding protein found in the muscle tissue of vertebrates in general and in almost all mammals. It is related to hemoglobin, which is the iron- and oxygen-binding protein in blood, specifically in the red blood cells. The only time myoglobin is found in the...

, an oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

-binding molecule, which tuna express in quantities far higher than most other fish. Some larger tuna species, such as bluefin tuna, display some warm-blooded
Warm-blooded
The term warm-blooded is a colloquial term to describe animal species which have a relatively higher blood temperature, and maintain thermal homeostasis primarily through internal metabolic processes...

 adaptations, and can raise their body temperatures above water temperatures by means of muscular activity. This enables them to survive in cooler waters and to inhabit a wider range of ocean environments than other types of fish.

Etymology

"Tuna" is akin to the Spanish word atún, this one coming from Spanish/Arabic "attún", derived from Latin thunnus / Greek θύννος, thynnos.

Taxonomy

There are over fifty different "tuna" species, the "tuna" designation often varying in accordance with local custom. The Thunnus
Thunnus
Thunnus is a genus of ocean-dwelling fish in the family Scombridae, all of which are tuna, although other tuna species are found in other genera. The name of the genus is the Latinized form of the Greek θύννος, thýnnos, tuna, the word being first mentioned in Homer...

 genus has been attributed to the species:
  • Albacore
    Albacore
    The albacore, Thunnus alalunga, is a type of tuna in the family Scombridae. This species is also called albacore fish, albacore tuna, albicore, longfin, albies, pigfish, tombo ahi, binnaga, Pacific albacore, German bonito , longfin tuna, longfin tunny, or even just tuna...

    , Thunnus alalunga (Bonnaterre
    Pierre Joseph Bonnaterre
    Abbé Pierre Joseph Bonnaterre was a French naturalist who contributed sections on cetaceans, mammals, birds, reptiles, amphibians, and insects to the Tableau encyclopédique et méthodique...

    , 1788)
    .
  • Yellowfin tuna
    Yellowfin tuna
    The yellowfin tuna is a species of tuna found in pelagic waters of tropical and subtropical oceans worldwide.Yellowfin is often marketed as ahi, from its Hawaiian name ahi although the name ahi in Hawaiian also refers to the closely related bigeye tuna. The species name, albacares can lead to...

    , Thunnus albacares (Bonnaterre
    Pierre Joseph Bonnaterre
    Abbé Pierre Joseph Bonnaterre was a French naturalist who contributed sections on cetaceans, mammals, birds, reptiles, amphibians, and insects to the Tableau encyclopédique et méthodique...

    , 1788)
    .
  • Blackfin tuna
    Blackfin tuna
    Blackfin tuna is the smallest tuna species in the Thunnus genus, generally growing to a maximum of in length and weighing 21 kg . Blackfin have oval shaped bodies, black backs with a slight yellow on the finlets, and have yellow on the sides of their body...

    , Thunnus atlanticus (Lesson
    René-Primevère Lesson
    René Primevère Lesson was a French surgeon, naturalist, ornithologist, and herpetologist.Lesson was born at Rochefort, and at the age of sixteen he entered the Naval Medical School there...

    , 1831)
    .
  • Southern bluefin tuna
    Southern bluefin tuna
    The southern bluefin tuna, Thunnus maccoyii, is a tuna of the family Scombridae found in open southern hemisphere waters of all the world's oceans mainly between 30°S and 50°S, to nearly 60°S...

    , Thunnus maccoyii (Castelnau, 1872).
  • Bigeye tuna
    Bigeye tuna
    The bigeye tuna, Thunnus obesus, is an important food fish and prized recreational game fish. It is a true tuna of the genus Thunnus, belonging to the wider mackerel family Scombridae....

    , Thunnus obesus (Lowe, 1839).
  • Pacific bluefin tuna
    Pacific bluefin tuna
    Pacific bluefin tuna, Thunnus orientalis are some of the biggest and fastest fish in the Pacific Ocean.They possess streamlined bodies to reduce water resistance and conserve energy for trans-Pacific migrations...

    , Thunnus orientalis (Temminck
    Coenraad Jacob Temminck
    Coenraad Jacob Temminck was a Dutch aristocrat and zoologist.Temminck was the first director of the National Natural History Museum at Leiden from 1820 until his death. His Manuel d'ornithologie, ou Tableau systematique des oiseaux qui se trouvent en Europe was the standard work on European birds...

     & Schlegel
    Hermann Schlegel
    Hermann Schlegel was a German ornithologist and herpetologist.-Early life and education:Schlegel was born at Altenburg, the son of a brassfounder. His father collected butterflies, which stimulated Schlegel's interest in natural history...

    , 1844)
    .
  • Northern bluefin tuna
    Northern bluefin tuna
    The Northern bluefin tuna is a species of tuna in the Scombridae family. It is variously known as the Atlantic bluefin tuna, giant bluefin tuna and formerly as the tunny. Atlantic bluefin are native to both the western and eastern Atlantic Ocean, as well as the Mediterranean Sea...

    , Thunnus thynnus (Linnaeus
    Carolus Linnaeus
    Carl Linnaeus , also known after his ennoblement as , was a Swedish botanist, physician, and zoologist, who laid the foundations for the modern scheme of binomial nomenclature. He is known as the father of modern taxonomy, and is also considered one of the fathers of modern ecology...

    , 1758)
    .
  • Longtail tuna, Thunnus tonggol (Bleeker
    Pieter Bleeker
    Pieter Bleeker was a Dutch medical doctor and ichthyologist, famous for his work on the fishes of East Asia – Atlas Ichthyologique des Orientales Neerlandaises – which was published 1862–1877....

    , 1851)
    .

Species of several other genera (all in the family Scombridae
Scombridae
Scombridae is the family of the mackerels, tunas, and bonitos, and thus includes many of the most important and familiar food fishes. The family consists of about 55 species in 15 genera and two subfamilies...

) have common names containing "tuna":
  • Slender tuna
    Slender tuna
    The slender tuna, Allothunnus fallai, is a species of tuna, the only species in the genus Allothunnus, found around the world in the southern oceans between latitudes 20° and 50° South...

     Allothunnus fallai (Serventy, 1948)
  • Bullet tuna
    Bullet tuna
    The bullet tuna, Auxis rochei rochei, is a subspecies of tuna, in the family Scombridae, found circumglobally in tropical oceans in open surface waters to depths of 50m . Its maximum length is 50.0 cm....

     Auxis rochei (Risso, 1810)
  • Terriowipet tuna Auxis tongolis (Bonnaterre
    Pierre Joseph Bonnaterre
    Abbé Pierre Joseph Bonnaterre was a French naturalist who contributed sections on cetaceans, mammals, birds, reptiles, amphibians, and insects to the Tableau encyclopédique et méthodique...

    , 1788)
    .
  • Frigate tuna
    Frigate tuna
    The frigate tuna or frigate mackerel, Auxis thazard thazard, is a subspecies of tuna, in the family Scombridae, found around the world in tropical oceans.-References:...

     Auxis thazard (Lacepede, 1800)
  • Kawakawa (little tuna or mackerel tuna) Euthynnus affinis (Cantor, 1849)
  • Little tunny
    Little tunny
    The little tunny is the most common tuna in the Atlantic Ocean. It is found in warm temperate and tropical waters of the Atlantic and the Mediterranean; in the western Atlantic, it ranges from Brazil to the New England states. It is found regularly in offshore and inshore waters, and is...

     (little tuna) Euthynnus alletteratus (Rafinesque, 1810)
  • Black skipjack tuna Euthynnus lineatus (Kishinouye, 1920)
  • Dogtooth tuna
    Dogtooth tuna
    The dogtooth tuna is a large fast-swimming fish in the family Scombridae. It is placed in its own genus, Gymnosarda. It has the large teeth and straight edged first dorsal fin characteristic of the smaller bonitos and although it far exceeds them in size, reaching weights of over 150 kilograms, is...

     Gymnosarda unicolor (Rüppell, 1836)
  • Skipjack tuna
    Skipjack tuna
    The skipjack tuna, Katsuwonus pelamis, is a medium-sized perciform fish in the tuna family, Scombridae. It is otherwise known as the aku, arctic bonito, mushmouth, oceanic bonito, striped tuna, or victor fish...

     Katsuwonus pelamis (Linnaeus
    Carolus Linnaeus
    Carl Linnaeus , also known after his ennoblement as , was a Swedish botanist, physician, and zoologist, who laid the foundations for the modern scheme of binomial nomenclature. He is known as the father of modern taxonomy, and is also considered one of the fathers of modern ecology...

    , 1758)

Biology

A remarkable aspect of Thunnus physiology is its ability to maintain body temperature above that of the ambient seawater. For example, bluefin can maintain a core body temperature of 75–95 °F (23.9–35 C), in water as cold as 43 °F (6.1 °C). However, unlike typical endothermic creatures such as mammals and birds, tuna do not maintain temperature within a relatively narrow range.

Tuna achieve endothermy by conserving the heat generated through normal metabolism. The rete mirabile
Rete mirabile
A rete mirabile is a complex of arteries and veins lying very close to each other, found in some vertebrates. The rete mirabile utilizes countercurrent blood flow within the net...

 ("wonderful net"), the intertwining of veins and arteries in the body's periphery, transfers heat from venous blood
Venous blood
Venous blood is deoxygenated blood in the circulatory system. It runs in the systemic veins from the organs to the heart. Deoxygenated blood is then pumped by the heart to lungs via the pulmonary arteries, one of the few arteries in the body that carries deoxygenated blood .Venous blood is...

 to arterial blood
Arterial blood
Arterial blood is the oxygenated blood in the circulatory system found in the lungs, the left chambers of the heart, and in the arteries. It is bright red in color, while venous blood is dark red in color...

 via a counter-current exchange system. This reduces surface cooling, maintaining warmer muscles. This supports higher swimming speed with reduced energy expenditure.

Commercial fishing

Tuna is an important commercial fish
Commercial fishing
Commercial fishing is the activity of catching fish and other seafood for commercial profit, mostly from wild fisheries. It provides a large quantity of food to many countries around the world, but those who practice it as an industry must often pursue fish far into the ocean under adverse conditions...

. The International Seafood Sustainability Foundation compiled a detailed scientific report on the state of global tuna stocks in 2009, which includes regular updates. According to the report, Tunas are widely but sparsely distributed throughout the oceans of the world, generally in tropical and temperate waters between about 45 degrees north and south of the equator. They are
grouped taxonomically in the family Scombridae, which includes about 50 species. The most important of these for commercial and recreational fisheries are yellowfin (Thunnus albacares), bigeye (T. obesus), bluefin (T. thynnus, T. orientalis, and T. macoyii), albacore (T. alalunga), and skipjack (Katsuwonus pelamis).

The report further states:

Japan's Fisheries Research Agency counters that Australian and New Zealand tuna fishing companies under-report their total catches of southern bluefin tuna and ignore internationally mandated total allowable catch totals.

In 2010, a bluefin tuna weighing 232 kilograms (511.47 pounds) was sold at Tokyo's Tsukiji fish market
Tsukiji fish market
The , commonly known as the , is the biggest wholesale fish and seafood market in the world and also one of the largest wholesale food markets of any kind. The market is located in Tsukiji in central Tokyo, and is a major attraction for foreign visitors....

 for 16.28 million yen ($US 175,000).

In early 2011, a new record was set at 32.49 million yen for a bluefin tuna weighing 342 kilograms (754 pounds), during an auction in Tsukiji Market, Tokyo. This equates to 95,000 yen per kilogram.

In November 2011 A Massachusetts fisherman pulled in an 881-pound tuna. It was caught on mistake using nets made to catch bottom dwelling fish. Due to the tough laws and restrictions on Tuna fishing,the Federal fishery enforcment had to take controle of the fish because it was not caught with a rod and reel.

Fishing methods

  • Andalusian method of Almadraba
    Almadraba
    Almadraba tuna is tuna caught by an elaborate and age-old Andalusian technique of setting nets in a maze that leads to a central pool called "copo". In Sicily, the mazes of nets, and also the places where the nets are set are called Tonnara, and the overall method of capturing the fishes is called...

    , uses a maze of nets. In Sicily, the same method is called Tonnara.
  • Fish farming (Cage system)
  • Longline fishing
  • Purse seines
  • Pole and line
  • Harpoon gun
  • Big game fishing
  • Fish aggregating device

Association with whaling

In 2005 Nauru
Nauru
Nauru , officially the Republic of Nauru and formerly known as Pleasant Island, is an island country in Micronesia in the South Pacific. Its nearest neighbour is Banaba Island in Kiribati, to the east. Nauru is the world's smallest republic, covering just...

, defending its vote at that year's meeting of the International Whaling Commission
International Whaling Commission
The International Whaling Commission is an international body set up by the terms of the International Convention for the Regulation of Whaling , which was signed in Washington, D.C...

, argued that commercial whaling is necessary for preserving tuna stocks and that country's fishing fleet.

Association with dolphins

Dolphin
Dolphin
Dolphins are marine mammals that are closely related to whales and porpoises. There are almost forty species of dolphin in 17 genera. They vary in size from and , up to and . They are found worldwide, mostly in the shallower seas of the continental shelves, and are carnivores, mostly eating...

s swim beside several tuna species. These include yellowfin tuna
Yellowfin tuna
The yellowfin tuna is a species of tuna found in pelagic waters of tropical and subtropical oceans worldwide.Yellowfin is often marketed as ahi, from its Hawaiian name ahi although the name ahi in Hawaiian also refers to the closely related bigeye tuna. The species name, albacares can lead to...

 in the eastern Pacific Ocean, but not albacore
Albacore
The albacore, Thunnus alalunga, is a type of tuna in the family Scombridae. This species is also called albacore fish, albacore tuna, albicore, longfin, albies, pigfish, tombo ahi, binnaga, Pacific albacore, German bonito , longfin tuna, longfin tunny, or even just tuna...

. Tuna schools are believed to associate themselves with dolphins for protection against sharks, which are tuna predators.

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, however the nets were prone to entangling dolphins, injuring or killing them. Public outcry and new government regulations, which are now monitored by the NOAA have led to more "dolphin friendly" methods, now generally involving lines rather than nets. However, there are neither universal independent inspection programs nor verification of "dolphin safeness", so these protections are not absolute. According to Consumers Union
Consumers Union
Consumers Union is a non-profit organization best known as the publisher of Consumer Reports, based in the United States. Its mission is to "test products, inform the public, and protect consumers."...

, the resulting lack of accountability means claims that tuna that is "dolphin safe
Dolphin safe label
There are various dolphin safe labels used for canned tuna to imply that the fish has been caught without harming or killing dolphins. However, because there are various labels used, there are also various restrictions imposed on the capture of tuna in order for it to deserve the related dolphin...

" should be given little credence.

Fishery practices have changed to be dolphin friendly, which has caused greater bycatch
Bycatch
The term “bycatch” is usually used for fish caught unintentionally in a fishery while intending to catch other fish. It may however also indicate untargeted catch in other forms of animal harvesting or collecting...

 including shark
Shark
Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago....

s, turtle
Turtle
Turtles are reptiles of the order Testudines , characterised by a special bony or cartilaginous shell developed from their ribs that acts as a shield...

s 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.

Management and conservation

There are five main tuna fishery management bodies: the Western Central Pacific Ocean Fisheries Commission, the Inter-American Tropical Tuna Commission
Inter-American Tropical Tuna Commission
The Inter-American Tropical Tuna Commission is an international commission that is responsible for the conservation and management of tuna and other marine resources in the eastern Pacific Ocean.-History:The Inter-American Tropical Tuna Commission was created by the Convention for the...

, the Indian Ocean Tuna Commission, the International Commission for the Conservation of Atlantic Tunas
International Commission for the Conservation of Atlantic Tunas
The International Commission for the Conservation of Atlantic Tunas is an intergovernmental organisation responsible for the management and conservation of tunas and tuna-like species in the Atlantic Ocean and adjacent seas. The organization was established in 1969, at a conference in Rio de...

 and the Commission for the Conservation of Southern Bluefin Tuna. The five gathered for the first time in Kobe
Kobe
, pronounced , is the fifth-largest city in Japan and is the capital city of Hyōgo Prefecture on the southern side of the main island of Honshū, approximately west of Osaka...

, Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...

 in January 2007. Environmental organizations made submissions on risks to fisheries and species. The meeting concluded with an action plan drafted by some 60 countries or areas. Concrete steps include issuing certificates of origin to prevent illegal fishing and greater transparency in the setting of regional fishing quotas. The delegates are scheduled to meet at another joint meeting in January or February 2009 in Europe.

In 2010, Greenpeace
Greenpeace
Greenpeace is a non-governmental environmental organization with offices in over forty countries and with an international coordinating body in Amsterdam, The Netherlands...

 International has added the albacore
Albacore
The albacore, Thunnus alalunga, is a type of tuna in the family Scombridae. This species is also called albacore fish, albacore tuna, albicore, longfin, albies, pigfish, tombo ahi, binnaga, Pacific albacore, German bonito , longfin tuna, longfin tunny, or even just tuna...

, bigeye tuna
Bigeye tuna
The bigeye tuna, Thunnus obesus, is an important food fish and prized recreational game fish. It is a true tuna of the genus Thunnus, belonging to the wider mackerel family Scombridae....

, blackfin tuna
Blackfin tuna
Blackfin tuna is the smallest tuna species in the Thunnus genus, generally growing to a maximum of in length and weighing 21 kg . Blackfin have oval shaped bodies, black backs with a slight yellow on the finlets, and have yellow on the sides of their body...

, pacific bluefin tuna
Pacific bluefin tuna
Pacific bluefin tuna, Thunnus orientalis are some of the biggest and fastest fish in the Pacific Ocean.They possess streamlined bodies to reduce water resistance and conserve energy for trans-Pacific migrations...

, northern bluefin tuna
Northern bluefin tuna
The Northern bluefin tuna is a species of tuna in the Scombridae family. It is variously known as the Atlantic bluefin tuna, giant bluefin tuna and formerly as the tunny. Atlantic bluefin are native to both the western and eastern Atlantic Ocean, as well as the Mediterranean Sea...

, southern bluefin tuna
Southern bluefin tuna
The southern bluefin tuna, Thunnus maccoyii, is a tuna of the family Scombridae found in open southern hemisphere waters of all the world's oceans mainly between 30°S and 50°S, to nearly 60°S...

 and the yellowfin tuna
Yellowfin tuna
The yellowfin tuna is a species of tuna found in pelagic waters of tropical and subtropical oceans worldwide.Yellowfin is often marketed as ahi, from its Hawaiian name ahi although the name ahi in Hawaiian also refers to the closely related bigeye tuna. The species name, albacares can lead to...

 to its seafood red list. "The Greenpeace International seafood red list is a list of fish that are commonly sold in supermarkets around the world, and which have a very high risk of being sourced from unsustainable fisheries."

It is widely accepted that bluefin tuna have been severely overfished
Overfishing
Overfishing occurs when fishing activities reduce fish stocks below an acceptable level. This can occur in any body of water from a pond to the oceans....

, with some stocks at risk of collapse. According to the International Seafood Sustainability Foundation (a global, non-profit partnership between the tuna industry, scientists, and the World Wide Fund for Nature
World Wide Fund for Nature
The World Wide Fund for Nature is an international non-governmental organization working on issues regarding the conservation, research and restoration of the environment, formerly named the World Wildlife Fund, which remains its official name in Canada and the United States...

), Indian Ocean yellowfin tuna, Pacific Ocean (eastern & western) bigeye tuna
Bigeye tuna
The bigeye tuna, Thunnus obesus, is an important food fish and prized recreational game fish. It is a true tuna of the genus Thunnus, belonging to the wider mackerel family Scombridae....

, and North Atlantic albacore
Albacore
The albacore, Thunnus alalunga, is a type of tuna in the family Scombridae. This species is also called albacore fish, albacore tuna, albicore, longfin, albies, pigfish, tombo ahi, binnaga, Pacific albacore, German bonito , longfin tuna, longfin tunny, or even just tuna...

 tuna are all overfished. In April 2009, no stock of skipjack tuna
Skipjack tuna
The skipjack tuna, Katsuwonus pelamis, is a medium-sized perciform fish in the tuna family, Scombridae. It is otherwise known as the aku, arctic bonito, mushmouth, oceanic bonito, striped tuna, or victor fish...

 (which makes up roughly 60 percent of all tuna fished worldwide) was considered to be overfished.

Aquaculture

Increasing quantities of high-grade tuna are reared in net pens and fed bait fish. In Australia, former fishermen raise southern bluefin tuna
Southern bluefin tuna
The southern bluefin tuna, Thunnus maccoyii, is a tuna of the family Scombridae found in open southern hemisphere waters of all the world's oceans mainly between 30°S and 50°S, to nearly 60°S...

, Thunnus maccoyii, and another bluefin species. Farming its close relative, the northern bluefin tuna
Northern bluefin tuna
The Northern bluefin tuna is a species of tuna in the Scombridae family. It is variously known as the Atlantic bluefin tuna, giant bluefin tuna and formerly as the tunny. Atlantic bluefin are native to both the western and eastern Atlantic Ocean, as well as the Mediterranean Sea...

, Thunnus thynnus, is beginning in the Mediterranean, North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...

 and Japan. Hawaii
Hawaii
Hawaii is the newest of the 50 U.S. states , and is the only U.S. state made up entirely of islands. It is the northernmost island group in Polynesia, occupying most of an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of...

 just approved permits for the first U.S. offshore farming of bigeye tuna
Bigeye tuna
The bigeye tuna, Thunnus obesus, is an important food fish and prized recreational game fish. It is a true tuna of the genus Thunnus, belonging to the wider mackerel family Scombridae....

 in water 1300 feet (396.2 m) deep.

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. The farm breed is known as Kindai tuna. Kindai is the contraction of Kinki University in Japanese (Kinki daigaku). In 2009, Clean Seas, an Australian company which has been receiving assistance from Kinki University managed to breed Southern Bluefin Tuna in captivity and was awarded the second place in World's Best Invention of 2009 by Time magazine.

Canned

Canned
Canning
Canning is a method of preserving food in which the food contents are processed and sealed in an airtight container. Canning provides a typical shelf life ranging from one to five years, although under specific circumstances a freeze-dried canned product, such as canned, dried lentils, can last as...

 tuna was first produced in 1903, quickly becoming popular. Tuna is canned in edible oil
Oil
An oil is any substance that is liquid at ambient temperatures and does not mix with water but may mix with other oils and organic solvents. This general definition includes vegetable oils, volatile essential oils, petrochemical oils, and synthetic oils....

s, in brine
Brine
Brine is water, saturated or nearly saturated with salt .Brine is used to preserve vegetables, fruit, fish, and meat, in a process known as brining . Brine is also commonly used to age Halloumi and Feta cheeses, or for pickling foodstuffs, as a means of preserving them...

, in water, in various sauces. In the United States, 52% of canned tuna is used for sandwiches; 22% for salad
Tuna salad
Tuna salad is typically a blend of two main ingredients: tuna and mayonnaise or mayonnaise-substitute. Chopped hard-boiled egg, celery or relish, and onion are ingredients that are often added. Tuna salad is regularly served on top of lettuce, tomato, avocado, or some combination of these...

s; and 15% for casserole
Tuna casserole
Tuna casserole is a casserole mainly composed of egg noodles and canned tuna fish, with canned peas and corn sometimes added. The casserole is often topped with potato chips, corn flakes or canned fried onions. It is a common dish in some parts of the United States of America...

s and dried, packaged meal mixes.

In the United States, only Albacore can legally be sold in canned form as "white meat tuna"; in other countries, yellowfin is also acceptable. While in the early 1980s canned tuna in Australia was most likely Southern bluefin
Southern bluefin tuna
The southern bluefin tuna, Thunnus maccoyii, is a tuna of the family Scombridae found in open southern hemisphere waters of all the world's oceans mainly between 30°S and 50°S, to nearly 60°S...

, it was usually yellowfin, skipjack, or tongol (labelled "northern bluefin").

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 pre-cooked for prescribed times of perhaps 45 minutes to three hours. The fish are then cleaned and filleted
Fillet (cut)
A fillet is a cut or slice of boneless meat or fish.- Meat :In the case of beef, in the USA, the term most often refers to beef tenderloin, especially filet mignon.- Chicken :...

, canned, and sealed, with the dark lateral blood meat often separately canned for pet food. The sealed can itself is then heated (called retort cooking) for 2 to 4 hours. This process kills any bacteria, but retains the histamine
Histamine
Histamine is an organic nitrogen compound involved in local immune responses as well as regulating physiological function in the gut and acting as a neurotransmitter. Histamine triggers the inflammatory response. As part of an immune response to foreign pathogens, histamine is produced by...

 that can produce rancid flavors. The international standard sets the maximum histamine level at 200 milligrams per kilogram. An Australian study of 53 varieties of unflavored canned tuna found none to exceed the safe histamine level, although some had "off" flavors.

Australian standards once required cans of tuna to contain at least 51% tuna, but these regulations were dropped in 2003. The remaining weight is usually oil or water. In the US
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

, the FDA
Food and Drug Administration
The Food and Drug Administration is an agency of the United States Department of Health and Human Services, one of the United States federal executive departments...

 regulates canned tuna (see part c). In 2008, some tuna cans changed from 6 ounces (170.1 g) to 5 ounces (141.7 g) due to "higher tuna costs".

Nutrition and health

Canned tuna can be a good source of omega-3 fatty acids. It sometimes contains over 300 milligram (0.0105821886315336 oz) per serving.

Mercury levels

Mercury content in tuna can vary widely. For instance, testing by Rutgers University reportedly found that a can of StarKist had 10 times more mercury than another can of similarly-identified tuna. This has prompted a Rutgers University scientist whose staff conducted the mercury analysis to say, "That's one of the reasons pregnant women have to be really careful ... If you happen to get a couple or three cans in the high range at a critical period when you are pregnant, it would not be good." Among those calling for improved warnings about mercury in tuna is the American Medical Association
American Medical Association
The American Medical Association , founded in 1847 and incorporated in 1897, is the largest association of medical doctors and medical students in the United States.-Scope and operations:...

, which adopted a policy that physicians should help make their patients more aware of the potential risks.

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. These findings suggest that choosing to consume a type of tuna that has a relatively higher natural fat content might help reduce the amount of mercury intake, compared to consuming tuna with a low fat content.

The industry-sponsored group Center for Consumer Freedom, which doesn't release the names of its contributors, claims the health risks of methylmercury
Methylmercury
Methylmercury is an organometallic cation with the formula . It is a bioaccumulative environmental toxicant.-Structure:...

 in tuna might be dampened by the selenium
Selenium
Selenium is a chemical element with atomic number 34, chemical symbol Se, and an atomic mass of 78.96. It is a nonmetal, whose properties are intermediate between those of adjacent chalcogen elements sulfur and tellurium...

 found in tuna, although the mechanism and effect of this still is largely unknown.

Due to their high position in the food chain and the subsequent accumulation
Biomagnification
Biomagnification, also known as bioamplification or biological magnification, is the increase in concentration of a substance that occurs in a food chain as a consequence of:* Persistence...

 of heavy metals
Heavy metals
A heavy metal is a member of a loosely-defined subset of elements that exhibit metallic properties. It mainly includes the transition metals, some metalloids, lanthanides, and actinides. Many different definitions have been proposed—some based on density, some on atomic number or atomic weight,...

 from their diet, mercury
Mercury (element)
Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...

 levels can be high in larger species such as bluefin and albacore
Albacore
The albacore, Thunnus alalunga, is a type of tuna in the family Scombridae. This species is also called albacore fish, albacore tuna, albicore, longfin, albies, pigfish, tombo ahi, binnaga, Pacific albacore, German bonito , longfin tuna, longfin tunny, or even just tuna...

.

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

In March 2004 the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 FDA
Food and Drug Administration
The Food and Drug Administration is an agency of the United States Department of Health and Human Services, one of the United States federal executive departments...

 issued guidelines recommending that pregnant women, nursing mothers, and children limit their intake of tuna and other predatory fish.

In 2007 it was reported that some canned light tuna such as yellowfin tuna
Yellowfin tuna
The yellowfin tuna is a species of tuna found in pelagic waters of tropical and subtropical oceans worldwide.Yellowfin is often marketed as ahi, from its Hawaiian name ahi although the name ahi in Hawaiian also refers to the closely related bigeye tuna. The species name, albacares can lead to...

 is significantly higher in mercury than skipjack, and caused Consumers Union
Consumers Union
Consumers Union is a non-profit organization best known as the publisher of Consumer Reports, based in the United States. Its mission is to "test products, inform the public, and protect consumers."...

 and other activist groups to advise pregnant women to refrain from consuming canned tuna.

The Eastern little tuna (Euthynnus affinis
Euthynnus affinis
Euthynnus affinis, the kawakawa, little or mackerel tuna or false albacore, is a fish species.-See also:* List of fish in India* List of fishes of the Red Sea* List of fish of Hawaii...

) has been available for decades as a low-mercury, less expensive canned tuna. However, of the five major species of canned tuna imported by the United States it is the least commercially attractive, primarily due to its dark color and more pronounced 'fishy' flavor. Its use has traditionally been restricted to institutional (non-retail) commerce.

A January 2008 investigation conducted by the New York Times found potentially dangerous levels of mercury
Mercury (element)
Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...

 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."

Further reading

  • Clover, Charles. 2004. The End of the Line: How Overfishing Is Changing the World and What We Eat
    The End of the Line: How Overfishing Is Changing the World and What We Eat
    The End of The Line: How Overfishing Is Changing the World And What We Eat is a book by journalist Charles Clover about overfishing. Clover, an environment editor of the Daily Telegraph , describes how modern fishing is destroying ocean ecosystems. He concludes that current worldwide fish...

    . Ebury Press, London. ISBN 0-09-189780-7
  • FAO
    Fão
    Fão is a town in Esposende Municipality in Portugal....

    : Species Catalog Vol. 2 Scombrids of the World. FAO Fisheries Synopsis No. 125, Volume 2. FIR/S125 Vol. 2.ISBN 92-5-101381-0
  • FAO
    Fão
    Fão is a town in Esposende Municipality in Portugal....

    : Review of the state of world marine fishery resources: Tuna and tuna-like species - Global, 2005 Rome.
  • Standard of Identity for Canned Tuna (United States), Code of Federal Regulations: 21 CFR 161.190 - Canned tuna.

External links

  • Atuna.com - tuna market gateway
  • Nutritional benefits of tuna
  • Tuna at Greenpeace
    Greenpeace
    Greenpeace is a non-governmental environmental organization with offices in over forty countries and with an international coordinating body in Amsterdam, The Netherlands...



  • Tuna at Stanford University Microdocs

News

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