Bluefin tuna, Thunnus thynnus, are found worldwide, mostly in temperate and subtropical waters. It is an important food fish. Tuna are among the largest, most specialized and most commercially important, of all fish. The bluefin is the largest of seven species. Some specimens exceed 14 feet (4.2 m) in length and 1,500 pounds (680 kg) in weight. Tuna typically have streamlined bodies with two dorsal fins, the first spiny and the second soft-rayed, followed by finlets and a large deeply forked tail. Fast swimmers, they travel at more than 30 miles per hour (48 km per hour) and typically migrate long distances and appear seasonally in any one location. They occur both in surface waters and at great depths.