A tuna (also called tunny) 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: 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 up to 50 years.