Tuna, belonging to the genus Thunnus , encompasses seven species of ocean-dwelling fish. They are commercially valuable and related to mackerels, residing in the Scombridae family. Tunas possess streamlined bodies, tapering to a slender tail base with a forked tail. They are generally dark on top and silvery below, often having an iridescent shine. Tunas undertake long migrations across the oceans, inhabiting tropical, temperate, and cooler waters. They consume fish, squid, shellfish, and plankton. Albacore and yellowfin tuna are commonly canned and among the world’s most popular seafoods.

Where do tuna live in the ocean?

Tunas are migratory fish that live in tropical, temperate, and even some cooler waters across the world's oceans. They can migrate long distances. The blackfin tuna has a limited distribution in the western Atlantic, while the longtail tuna lives in the Indo-Pacific region.

Tunas consume a varied diet that includes fishes, squid, shellfish, and various planktonic organisms . They are migratory fish found worldwide in tropical, temperate, and cooler waters. The blackfin tuna and the longtail tuna are the only two species with limited distribution.

How are tuna different from other fish?

Tunas, belonging to the genus Thunnus , are distinct from other fish species due to their unique physiological adaptations and physical characteristics. They are streamlined, robust, and elongated, with a slender tail base and a forked or crescent-shaped tail. Tunas possess a specialized network of blood vessels beneath their skin that regulates their body temperature, allowing them to maintain it at a higher level than the surrounding water. This adaptation enables them to thrive in a wide range of ocean temperatures across the world. Tunas are generally dark on their upper side and silvery below, often with an iridescent shine. They also have a conspicuous keel on either side of the tail base, a row of small finlets behind the dorsal and anal fins, and a corselet of enlarged scales in the shoulder region.

Why are tuna important to people?

Tuna, belonging to the genus Thunnus , are of great commercial value as food. They are elongated, robust, streamlined fishes with the ability to maintain their body temperature above the surrounding water temperature. Species such as northern bluefin, albacore, and yellowfin are harvested for their meat, which is canned and sold worldwide. However, overfishing has caused a significant decline in the populations of some tuna species, such as the northern bluefin tuna, leading to calls for harvesting moratoriums.

What are some challenges faced by tuna populations today?

Tuna populations face several challenges today, primarily stemming from commercial fishing activities. Overfishing has significantly decreased populations of the northern bluefin tuna in the Atlantic Ocean since preindustrial times. Some fishing practices also result in the killing of dolphins. Increasing population pressure and economic development in coastal regions have led to habitat impairment for many coastal species. Both Atlantic and Pacific stocks have been heavily fished since the end of World War II, and signs of excessive harvest have appeared.

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Images

Bluefin tuna swimming underwater in a group, with silvery bodies and streamlined shapes, near Japan.

Illustration of an albacore tuna (Thunnus alalunga), showing a streamlined fish with a blue back, silvery sides, yellowish fin, and long pectoral fins, measuring about 42 inches in length.

Illustration of a bluefin tuna (Thunnus thynnus), showing a large, streamlined fish with a dark blue back, silvery sides, and pointed fins, reaching up to 10 feet in length.

Illustration of a skipjack tuna (Katsuwonus pelamis), a streamlined fish about 3 feet long with a dark blue back, silvery sides, and distinct horizontal stripes along the lower body.

“Bluefin Tunas and the Problem of Overfishing”

At a Glance

tuna summary

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Also called:: tunny

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tuna

fish

Also known as: tunny

Written and fact-checked by

Britannica Editors

Last updated

Oct. 14, 2026 •History

Top Questions

What is a tuna fish?
Tuna, belonging to the genus Thunnus, encompasses seven species of ocean-dwelling fish. They are commercially valuable and related to mackerels, residing in the Scombridae family. Tunas possess streamlined bodies, tapering to a slender tail base with a forked tail. They are generally dark on top and silvery below, often having an iridescent shine.

Tunas undertake long migrations across the oceans, inhabiting tropical, temperate, and cooler waters. They consume fish, squid, shellfish, and plankton. Albacore and yellowfin tuna are commonly canned and among the world’s most popular seafoods.
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Where do tuna live in the ocean?
Tunas are migratory fish that live in tropical, temperate, and even some cooler waters across the world's oceans. They can migrate long distances. The blackfin tuna has a limited distribution in the western Atlantic, while the longtail tuna lives in the Indo-Pacific region.
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What do tuna eat?
Tunas consume a varied diet that includes fishes, squid, shellfish, and various planktonic organisms. They are migratory fish found worldwide in tropical, temperate, and cooler waters. The blackfin tuna and the longtail tuna are the only two species with limited distribution.
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2. albacore
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How are tuna different from other fish?
Tunas, belonging to the genus Thunnus, are distinct from other fish species due to their unique physiological adaptations and physical characteristics. They are streamlined, robust, and elongated, with a slender tail base and a forked or crescent-shaped tail. Tunas possess a specialized network of blood vessels beneath their skin that regulates their body temperature, allowing them to maintain it at a higher level than the surrounding water. This adaptation enables them to thrive in a wide range of ocean temperatures across the world.

Tunas are generally dark on their upper side and silvery below, often with an iridescent shine. They also have a conspicuous keel on either side of the tail base, a row of small finlets behind the dorsal and anal fins, and a corselet of enlarged scales in the shoulder region.
3 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
Why are tuna important to people?
Tuna, belonging to the genus Thunnus, are of great commercial value as food. They are elongated, robust, streamlined fishes with the ability to maintain their body temperature above the surrounding water temperature.

Species such as northern bluefin, albacore, and yellowfin are harvested for their meat, which is canned and sold worldwide. However, overfishing has caused a significant decline in the populations of some tuna species, such as the northern bluefin tuna, leading to calls for harvesting moratoriums.
1 Britannica Source
1. tuna
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
What are some challenges faced by tuna populations today?
Tuna populations face several challenges today, primarily stemming from commercial fishing activities. Overfishing has significantly decreased populations of the northern bluefin tuna in the Atlantic Ocean since preindustrial times. Some fishing practices also result in the killing of dolphins. Increasing population pressure and economic development in coastal regions have led to habitat impairment for many coastal species. Both Atlantic and Pacific stocks have been heavily fished since the end of World War II, and signs of excessive harvest have appeared.
3 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

tuna, (genus Thunnus), any of seven species of oceanic fishes, some very large, that constitute the genus Thunnus and are of great commercial value as food. They are related to mackerels and are placed with them in the family Scombridae (order Perciformes). Tunas vary considerably, both within and among species.

northern bluefin tunaNorthern bluefin tuna (Thunnus thynnus).

Tunas are elongated, robust, and streamlined fishes; they have a rounded body that tapers to a slender tail base and a forked or crescent-shaped tail. In colour, tunas are generally dark above and silvery below, often with an iridescent shine. They have a conspicuous keel on either side of the tail base, a row of small finlets behind dorsal and anal fins, and a corselet of enlarged scales in the shoulder region. Another notable feature is a well-developed network of blood vessels below the skin that acts as a temperature-regulating device associated with long-term, slow swimming. Because of this vascular system, tunas are unique among fishes in their ability to maintain the temperature of their bodies above that of the surrounding water, often between 5 and 12 °C (9 and 21.7 °F) above ambient water temperature. Some muscles may even be up to 21 °C (almost 39 °F) higher than the surrounding water.

The seven species of tunas in the genus Thunnus are the northern bluefin tuna (T. thynnus), albacore (T. alalunga), yellowfin tuna (T. albacares), southern bluefin tuna (T. thynnus maccoyii), bigeye tuna (T. obesus), blackfin tuna (T. atlanticus), and longtail tuna (T. tonggol). These different species range from moderate to very large in size. The giant of the group is the northern bluefin tuna, which grows to a maximum length and weight of about 4.3 metres (14 feet) and 800 kg (1,800 pounds). The yellowfin tuna reaches a maximum weight of about 180 kg (397 pounds), and the albacore grows to about 36 kg (79 pounds).

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The northern bluefin tuna characteristically has yellow finlets and is often marked with silvery spots or bars. It is important in sport and commercial fishing, with anglers rating it among the greatest trophies obtainable. Populations of northern bluefin tuna in the Atlantic Ocean have declined significantly since preindustrial times because of overfishing. As a result, many scientists and environmental organizations have called for a moratorium on the harvesting of this species. Such a ban, however, has yet to be implemented. The other commercially important species are the albacore, marked with a shining blue stripe on each side; the yellowfin, with yellow fins and a golden stripe on each side; and the bigeye, a robust fish with relatively large eyes.

Tunas migrate long distances over all the world’s oceans and occupy tropical, temperate, and even some cooler waters. The only two species of relatively limited distribution are the blackfin tuna (western Atlantic) and the longtail tuna (Indo-Pacific region). Tunas feed on fishes, squid, shellfish, and a variety of planktonic organisms. They spawn in the open sea over very large areas. The canned meat of albacore and yellowfin tunas is one of the world’s most popular seafoods. Measures were undertaken in the late 20th century to prevent large numbers of dolphins from being killed by the nets used to catch tuna in the world’s oceans.

Several other species in the family Scombridae are commonly known as tuna, among them the skipjack tuna (Katsuwonus, or Euthynnus, pelamis), a fish that is found worldwide and grows to about 90 cm (3 feet) and 23 kg (51 pounds). The bonitos, of the genus Sarda, are tunalike fishes found worldwide and have both commercial and sporting value.

The Editors of Encyclopaedia BritannicaThis article was most recently revised and updated by Adam Augustyn.

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