<Li> Katsuwonus: cocinal tunas </Li> <Li> Thunnus: albacores, true tunas </Li> <P> A tuna is a saltwater fish that belongs to the tribe Thunnini, a sub-grouping of the mackerel family (Scombridae). Thunnini comprises fifteen species across five genera, the sizes of which vary greatly, ranging from the bullet tuna (max. length: 50 cm (1.6 ft), weight: 1.8 kg (4 lb)) up to the Atlantic bluefin tuna (max. length: 4.6 m (15 ft), weight: 684 kg (1,508 lb)). The bluefin averages 2 m (6.6 ft), and is believed to live for up to 50 years . When canned and packaged for sale, the product is sometimes called tuna fish . </P> <P> Tuna and mackerel sharks are the only species of fish that can maintain a body temperature higher than that of the surrounding water . An active and agile predator, the tuna has a sleek, streamlined body, and is among the fastest - swimming pelagic fish--the yellowfin tuna, for example, is capable of speeds of up to 75 km / h (47 mph). Found in warm seas, it is extensively fished commercially, and is popular as a game fish . As a result of overfishing, stocks of some tuna species, such as the southern bluefin tuna, are close to extinction . </P>

How many different types of tuna are there