Tuna

The Atlantic bluefin tuna (Thunnus thynnus) is a species of tuna in the family Scombridae. Atlantic bluefins are native to both the western and eastern Atlantic Ocean, as well as the Mediterranean Sea. They have become extinct in the Black Sea. The Atlantic bluefin tuna is a close relative of the other two bluefin tuna species—the Pacific bluefin tuna and the southern bluefin tuna.

Atlantic bluefin tuna have been recorded at up to 680 kg (1,500 lb) in weight, and rival the black marlin, blue marlin, and swordfish as the largest Perciformes. Throughout recorded history, the Atlantic bluefin tuna has been highly prized as a food fish. Besides their commercial value as food, the great size, speed, and power they display as apex predators has attracted the admiration of fishermen, writers, and scientists.

Most bluefins are captured commercially by professional fishermen using longlines, purse seines, assorted hook-and-line gear, heavy rods and reels, and harpoons. Recreationally, bluefins have been one of the most important big-game species sought by sports fishermen since the 1930s, particularly in the United States, but also in Canada, Spain, France, and Italy. 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.

Dolphins swim beside several tuna species. Tuna schools are believed to associate themselves with dolphins for protection against sharks, which are tuna predators. Bluefins dive to depths of 1,006 m (3,301 ft).] The Atlantic bluefin tuna typically hunts small fish such as sardines, herring, and mackerel, and invertebrates such as squid and crustaceans.

All tunas are able to maintain the temperature of certain parts of their body above the temperature of ambient seawater. For example, bluefin can maintain a core body temperature of 25–33 °C (77–91 °F), in water as cold as 6 °C (43 °F). However, unlike "typical" endothermic creatures such as mammals and birds, tuna do not maintain temperature within a relatively narrow range.

Also unlike most fish, which have white flesh, the muscle tissue of tuna ranges from pink to dark red. The red myotomal 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.

As a result of commercial overfishing, some tuna species, such as the southern bluefin tuna, are threatened with extinction and many other species are listed as vulnerable, nearly threatened, endangered, or critically endangered.

— Source: Wikipedia / Bellisseria Oceanographic Institute