Bluefin is a species of large fish known as tuna. Specifically, it refers to the various species of the Thunnus genus, including the Atlantic bluefin tuna (Thunnus thynnus) and the Pacific bluefin tuna (Thunnus orientalis). Bluefin tunas are highly prized for their meat and are popular in sushi and sashimi dishes. They are known for their large size, streamlined bodies, and remarkable swimming abilities, making them one of the fastest and most powerful fish in the ocean.