Description: The body of the yellowfin tuna tapers at both ends (cigar-shaped), and the head is conical. The color is dark brownish blue to dark yellow on the back becoming gray or whitish below. Identifying tunas can be difficult, especially when yellowfin and bigeye tuna are involved. In most cases, the length of the pectoral fins can distinguish each species. The yellowfin has pectoral fins which do not extend past the anal fin; while in bigeye, the pectoral fins extend well past the anal fin. Tuna which cannot be distinguished by external characteristics can be positively identified by liver characteristics. The surface of a yellowfin's liver is smooth while the liver of the bigeye is striated, containing many with small blood vessels along the trailing edge.