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,[2] the sizes of which vary greatly, ranging from the bullet tuna (max length: 50 cm or 1.6 ft, weight: 1.8 kg or 4 lb) up to the Atlantic bluefin tuna (max length: 4.6 m or 15 ft, weight: 684 kg or 1,508 lb), which averages 2 m (6.6 ft) and is believed to live up to 50 years.