The bluefin tuna is one of the largest of the tunas. The body is deepest near the insertion of the pelvic fins, and tapers significantly to the caudal peduncle. Compared to other tunas, the head is long and somewhat pointed, and the eye is small. Two dorsal fins are present, with a small space separating them. The second dorsal fin is taller than the first, and is followed by 7 to 10 finlets. The anal fin begins well behind the insertion of the second dorsal fin. The pectoral fins are short compared to other members of the genus Thunnus, although the relative length changes with age. The pectoral fins never reach as far back as the space between the dorsal fins. Three keels are present on the caudal peduncle. The body is a metallic deep blue above and the lower sides and belly are silvery white. In fresh specimens, alternating colorless lines and rows of dots can be seen along the lower sides. The first dorsal fin is yellow or blue, the second is red or brown. The anal fin and finlets are yellow, edged with black. The central caudal keel is black.