- published: 19 Jun 2013
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Tuna are a group of salt water fish from the family Scombridae, particularly of the genus Thunnus. Tuna are fast swimmers, and some species are capable of speeds of 70 km/h (43 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, an oxygen-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 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.
Altogether, over fifty different species, all belonging to the family Scombridae, are commonly referred to as tuna. The term tuna derives from Latin thunnus / Greek θύννος, thynnos.
True tuna belong to the genus Thunnus, or "tuna". There are eight species in the genus. Until recently, it was thought that there were only seven species, and that Atlantic bluefin tuna and the Pacific bluefin tuna were subspecies of the same species. In 1999 Collette established, on molecular and morphological considerations, that these are separate species.
A fish is any member of a paraphyletic group of organisms that consist of all gill-bearing aquatic craniate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups. Most fish are ectothermic ("cold-blooded"), allowing their body temperatures to vary as ambient temperatures change, though some of the large active swimmers like white shark and tuna can hold a higher core temperature. Fish are abundant in most bodies of water. They can be found in nearly all aquatic environments, from high mountain streams (e.g., char and gudgeon) to the abyssal and even hadal depths of the deepest oceans (e.g., gulpers and anglerfish). At 32,000 species, fish exhibit greater species diversity than any other group of vertebrates.
Fish are an important resource worldwide, especially as food. Commercial and subsistence fishers hunt fish in wild fisheries (see fishing) or farm them in ponds or in cages in the ocean (see aquaculture). They are also caught by recreational fishers, kept as pets, raised by fishkeepers, and exhibited in public aquaria. Fish have had a role in culture through the ages, serving as deities, religious symbols, and as the subjects of art, books and movies.