Bluefin and Yellowfin are two species of tuna that are commonly found in the ocean. Bluefin tuna are large, fast-swimming fish that can weigh up to 1, 500 pounds and reach lengths of up to 10 feet. Yellowfin tuna are smaller than bluefin, typically weighing between 20 and 80 pounds and reaching lengths of up to 6 feet. Both species are highly sought after for their meat, which is used in sushi, canned tuna, and other dishes.