<P> The Atlantic bluefin tuna (Thunnus thynnus) is a species of tuna in the family Scombridae . It is variously known as the northern bluefin tuna (mainly when including Pacific bluefin as a subspecies), giant bluefin tuna (for individuals exceeding 150 kilograms (330 lb)) and formerly as the tunny . </P> <P> Atlantic bluefin are native to both the western and eastern Atlantic Ocean, as well as the Mediterranean Sea . Atlantic bluefin 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 . </P> <P> Atlantic bluefin tuna may exceed 450 kg (990 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 . </P> <P> The Atlantic bluefin tuna has been the foundation of one of the world's most lucrative commercial fisheries . Medium - sized and large individuals are heavily targeted for the Japanese raw fish market, where all bluefin species are highly prized for sushi and sashimi . </P>

How big does a tuna have to be to keep