Northern bluefin tuna
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[Photo] Roter Thun, Roter Thunfisch oder Blauflossen-Thunfisch (Thunnus thynnus). National Oceanic & Atmospheric Adminstration (NOAA),Photo Library, http://www.photolib.noaa.gov

The northern bluefin tuna (Thunnus thynnus) is a species of tuna fish, living in both the Western and the Eastern Atlantic Ocean and extending into the Mediterranean Sea and the Black Sea. Although not native to the Pacific Ocean, it is cultivated off Japan. Northern bluefin tuna can live to be up to 30 years old. The typical size is 2 m (6.6 ft) at about 500 kg (1,100 lb). The largest recorded specimen was caught off Nova Scotia, and was recorded as weighing 679 kg (1,500 lb). Their maximum length is 14 feet. They are caught by sports fishermen using a heavy-duty rod and reel. The northern bluefin tuna is an important food fish used almost exclusively in sushi; canned tuna and tuna sold as steaks are of other species.

The species is also known as horse mackerel and in the past was called the common tunny. It is often referred to simply as the "bluefin" or "bluefin tuna", but this name is ambiguous as it is also sometimes used for the southern bluefin tuna, Thunnus maccoyii, and the Pacific bluefin tuna, T. orientalis. Even the preferred name, northern bluefin tuna, is not unambiguous, because this is sometimes used for the longtail tuna T. tonggol. In Australia, canned T. tonggol can and is legally sold under the name "Northern bluefin tuna".

The body of the northern bluefin tuna is cigar-shaped and robust. The head is conical and the mouth rather large. They typically prey on small fish such as sardines, herring, mackerel, squid and crustaceans. The color is dark blue above and gray below. Northern bluefin tuna can easily be distinguished from other members of the tuna family by the relatively short length of their pectoral fins. Their livers have a unique and definitive characteristic in that they are covered with blood vessels (striated). In other tunas with short pectoral fins, such vessels are either not present or present in small numbers along the edges.

The northern bluefin tuna is an important source of seafood, providing most of the tuna used in sushi. It is a particular delicacy in Japan where the price of a single giant tuna can exceed $100,000 on the Tsukiji fish market in Tokyo. It is also popular in Taiwan, particularly in the town of Tungkang. As a result, some fisheries of bluefin are considered overfished, and this problem is compounded by the bluefin's slow growth rate and late maturity. The Atlantic population of the species has declined by nearly 90 percent since the 1970s. The bluefin species are consequently listed as ones to "Avoid" on the Monterey Bay Aquarium's Seafood Watch program.

The tetraphyllidean tapeworm Pelichnibothrium speciosum has been found to parasitize this species (Scholz et al. 1998). As the tapeworm's definite host is the blue shark which does not generally seem to feed on tuna, it is likely that the northern bluefin tuna is a dead-end host for P. speciosum.

http://en.wikipedia.org/wiki/Northern_bluefin_tuna

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