Bluefin have a fusiform body, compressed and stocky in front. The pectoral fin does not reach the origin of the 2nd dorsal fin. The height of the 2nd dorsal fin is greater than that of the 1st dorsal fin. The liver is striated on the ventral surface, and a swimbladder is present. There are 34 to 43 gill rakers on the first gill arch. The back and upper sides are dark blue to black with a gray or green iridescence. The lower sides are silvery, marked with gray spots and bands. The 2nd dorsal fin is reddish-brown, and the anal fin is dusky with some yellow. The finlets are yellow, edged with black. The caudal keel is black at the adult stage, but is semitransparent when immature. Common size: 16 to 79 inches,