This species of tuna is easily identifiable by its two long yellow fins. It is found in the open waters of tropical and subtropical seas worldwide. It is an epipelagic fish ranging in the top 100 m (330 feet) of the water column. It has been reported to be up to 239 cm (94 inches) in length and 200 kg (440 lb) in weight. The fish is also known as ahi tuna, after the Hawaiian word for "fire", due to the smoke from their fishing ropes rubbing violently on the gunwales of their wooden canoes while pulling the fish in. They are becoming a popular replacement for bluefin tuna because of the yellowfin's low conservation threat level and the severe depletion of the number of bluefin tuna.
The second dorsal fin and the anal fin are both bright yellow, thus the common name, and can be very long in mature specimens, as are the pectoral fins. The main body is very dark metallic blue, changing to silver on the belly, which has about 20 vertical lines.
Yellowfins tend to school with fishes of the same size, including other species of tuna, and larger fish are often seen with dolphins, porpoises, whales and whale sharks. Yellowfins eat other fish, crustaceans, and squid.