Is Tuna a fish?

In this post, we will answer the question “Is Tuna a fish?” and also learn about the general characteristics of tuna, as well as its biology and ecology.

Is Tuna a fish?

Yes, Tuna refers to a genus of fish, Thunnus. The Tuna is one of the most important groups of fish species from a fishing point of view.

Tuna has a long, plump body. It is usually darker on the back and silverier on the belly. Some species have spots or stripes. Unlike most types of fish, tuna can maintain a warmer body temperature than the surrounding water.

Most tuna species are about 1 metre long. Although, Bluefin tuna can reach 4 metres in length and weigh up to 800 kilograms.

Tuna travel in large groups, called shoals. Some species swim great distances. Tuna feed on other fish, including herring, menhaden, and mackerel. Some species also eat small invertebrates such as squids. Various types of tuna return to the waters where they were born during the breeding season.

Tuna characteristics

They are inhabitants of tropical and subtropical oceanic regions, Tuna has an elongated, spindle-shaped body and a large, elongated mouth. Its dorsal fins are well spaced, adjustable to a groove on its back, while its bifurcated caudal fin has two keratin fins. The back of this fish has a dark blueish colour, while on the belly and flanks silver predominates.

A member of the Scombridae family and the genus Thunnus, this illustrious member of the Perciformes vascular system, specialized in heat exchange, can raise their body temperature between 10 and 15 degrees Celsius above environment temperature, making it an endothermic. This thermic capability gives him the ability to be a great swimmer, migrating across an ocean and reaching a distance of up to 170 km in a single day. 

Bluefin tuna is one of the few warm-blooded fish species. When it dives to great depths where the temperature can reach 5°C, it can keep its body temperature at 27°C, very close to that of mammals. Furthermore, it is among the fastest fish, being able to reach speeds close to 80 km/h and to cross entire oceans during migration.

This same vascular system gives a rosy hue to the tuna’s flesh, as the tuna’s metabolism allows the body’s muscles to also collaborate in collecting and filtering oxygen.

This fish is part of human history. It was represented through cave paintings by primitive men, and its image was even minted on coins. The first known reference to tuna fishing dates from 700 BC, in the Aegean Sea. Shoals served as food for the Greeks and, later, for Roman legions.

There are eight species of tuna, the Bluefin Tuna is the most popular. That is because the Bluefin Tuna has a remarkable size and extremely tasty meat.

Circulation and heat exchange

The exchange of heat using warm venous blood to raise the temperature of the new blood, until both are equivalent in heat, makes the internal temperature of the tuna higher than that of the waters it inhabits. Thus, granting it greater speed and reach in a trip, more than any other fish, besides being a great defence against the predators, bacteria, and fungi.


Tuna is a dioicous fish, with no apparent sexual dimorphism, and the female produces large amounts of planktonic eggs, which will become pelagic larvae. 


Tuna is a fish that lives in tropical and subtropical regions of all oceans. Usually, they only form schools of fish of the same age.

However, approaching the coast is not customary for these species. It is usually more common to find these fish in the open sea, except for deep areas. Tuna, especially the younger ones, tend to swim in shoals.

Predators and forms of defence

Among the tuna predators, it is possible to highlight sharks, seals, and sea lions as natural predators of tuna, but man also fits in this list.

Tuna is historical of great fishing importance, so there is no doubt that the biggest tuna predator is humans. Their fishing is and has always been, very popular.

For this reason, and as a result of the increased demand for fish on the international market, some tuna species, such as the “blue” tuna (Thunnus thynnus) have become overfished.

However, during the 20th century, several international organizations were formed that promote responsible tuna fishing, such as the International Commission for the Conservation of Atlantic Tuna and the Inter-American Commission for Tropical Tuna.

In addition to being consumed fresh, tuna is also an important raw material for the canning industry. In Portugal, this industry started to flourish at the end of the 19th century, consolidating its market position during the first half of the 20th century.

More recently, however, with the development of environmental movements, some environmental problems have been raised. Although tuna fisheries are quite specific, it was found that during some types of fishing, such as net fishing, some unwanted or even protected species were captured, such as sea turtles and dolphins.

For this reason, consumers (mainly in the United States, but also tending to become popular in the European Union) are advised not to purchase tuna that is not “certified” as coming from “responsible fishing” or “that protects biodiversity”.

Climate change and migration

Tuna species are highly migratory-they move large distances depending on ocean conditions. The species of skipjack, yellowfin, and bigeye tuna are found mainly in the waters of the Pacific islands.

The concentrations of these stocks typically change from year to year between areas further east in the El Niño years and that farther west in the La Niña years. However, due to climate change, these stocks are projected to move eastward—out of sovereign waters and out to sea.

With climate change, the tropical waters of the Pacific Ocean will warm even more. This warming will result in a major shift eastward in the location of the edge of the Western Pacific Warm Pool (a body of water in the western Pacific Ocean with consistently high-water temperatures) and subsequently the main fishing location for some tropical tuna.

The biggest tuna in the world

Bluefin tuna is considered the largest tuna in the world, it can measure up to 5 metres and weigh up to 700 kg. It feeds on fish, squid, pelagic crustaceans, and zooplankton. They usually hunt in groups, the school gathers in the shape of a parabola and is rapidly approaching the prey until there is no room for them to flee.

Although their species is known for hunting schools of small fish, their metabolism is adapted for high-speed chases. However, as an opportunistic predator, when it is hungry it will eat what is within its reach.

The tuna began to gain fame among the Japanese in the 70s. Due to the globalization of sushi and sashimi consumption, this species is threatened with extinction in some regions. This makes its commercial value even higher. Earlier this year, a 222-kilogram bluefin tuna was auctioned off in Tokyo for the record price of $ 1 million UD dollars.


In this post, we get to know about the characteristics of tuna as well as its biology and ecology.

If you have any thoughts or doubts, feel free to drop us in a comment below!

Frequently Asked Questions (FAQs): Is Tuna a fish?

What fish is tuna?

Tuna are large fish that live in almost every ocean. They belong to the same family as the fish called mackerel. Tuna is one of the most popular foods that come from the sea. Most of the tuna caught is industrialized and sold in cans.

Where is tuna found?

Tuna can be found worldwide. They inhabit almost every ocean tropical and subtropical waters..

What is the tuna predator? 

Among the tuna predators, it is possible to highlight sharks, seals, and sea lions as natural predators of tuna, but man also fits in this list, due to the great interest of the fishing industry in the species.

How long does tuna live?

In general, tuna can live up to 50 years old.

What is the size of a Bluefin tuna?

The bluefin tuna can grow up to 5 metres in length and weigh up to 700 kilograms

What are the different tuna species?

There are 15 tuna species, they are albacore, bigeye, black skipjack, blackfin, bluefin (three species: Atlantic, Pacific, southern), bullet, frigate, kawakawa, little tunny, longtail, skipjack, slender and yellowfin.


Schaefer, K. M. (2001). Reproductive biology of tunas. Fish Physiology, 19, 225-270.

Baglin, R. E. (1982). Reproductive biology of western Atlantic bluefin tuna. Fish. Bull, 80(1), 121-134.

Block, B. A., Dewar, H., Blackwell, S. B., Williams, T. D., Prince, E. D., Farwell, C. J., … & Fudge, D. (2001). Migratory movements, depth preferences, and thermal biology of Atlantic bluefin tuna. Science, 293(5533), 1310-1314.