A tuna is a saltwater fish that belongs to the tribe Thunnini, a subgrouping of the Scombridae (mackerel) family. The Thunnini comprise 15 species across five genera, the sizes of which vary greatly, ranging from the bullet tuna (max length: , weight: ) up to the Atlantic bluefin tuna (max length: , weight: ), which averages and is believed to live up to 50 years. Tuna, opah 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 . Greatly inflated speeds can be found in early scientific reports and are still widely reported in the popular literature. Found in warm seas, the tuna is commercially fished extensively as a food fish, and is popular as a bluewater game fish. As a result of overfishing, some tuna species, such as the southern bluefin tuna, are threatened with extinction. Etymology The term "tuna" comes from Spanish atún < Andalusian Arabic at-tūn, assimilated from al-tūn [Modern Arabic ] : 'tuna fish' < Middle Latin thunnus. is derived from used for the Atlantic bluefin tuna, that name in turn is ultimately derived from thýnō, meaning "to rush, dart along". Taxonomy The Thunnini tribe is a monophyletic clade comprising 15 species in five genera: family Scombridae tribe Thunnini: tunas genus Allothunnus: slender tunas genus Auxis: frigate tunas genus Euthynnus: little tunas genus Katsuwonus: skipjack tunas genus Thunnus: albacores and true tunas subgenus Thunnus (Thunnus): bluefin group subgenus Thunnus (Neothunnus): yellowfin group The cladogram is a tool for visualizing and comparing the evolutionary relationships between taxa, and is read left-to-right as if on a timeline. The following cladogram illustrates the relationship between the tunas and other tribes of the family Scombridae. For example, the cladogram illustrates that the skipjack tunas are more closely related to the true tunas than are the slender tunas (the most primitive of the tunas), and that the next nearest relatives of the tunas are the bonitos of the tribe Sardini. True species The "true" tunas are those that belong to the genus Thunnus. Until recently, it was thought that there were seven Thunnus species, and that Atlantic bluefin tuna and Pacific bluefin tuna were subspecies of a