The Bluefin Tuna (Thunnus thynnus) is a large bony fish and is the largest tuna. The Bluefin Tuna lives for about 40 years.
The Southern Bluefin Tuna is a species very similar to and closely related to the Bluefin Tuna. These two fish only differ internally. The Southern Bluefin lives in the Southern Hemisphere from about 30° to 50° Latitude South. They breed in the Indian Ocean near Indonesia. The Southern Bluefin Tuna has been overfished and is in danger of extinction.
Anatomy: The Bluefin Tuna is dark blue to almost black above and light silver below. There is a yellow line from the snout along half of the body. This yellow line disappears after death. The tail is dark blue. It typically grows to be about 6 ft (2 m) long and weighs about 300 pounds (135 kg). The heaviest known are about 1,200 pounds (550 kg). The Bluefin Tuna is mature at about 8 years old, when it has reached a length of about 5 feet (1.5 m).