The Bigeye Tuna's pectoral fins may reach to the second dorsal fin, but are shorter than the Yellowfin Tuna's. A very short pectoral fin indicates that the fish more than likely is a Bluefin Tuna.
There are 18 to 22 gill rakers on the first gill arch of a Bigeye Tuna. There will be 24 to 28 gill rakers on a Bluefin Tuna, and 27 to 33 gill rakers on a Yellowfin Tuna.
Positive identification of a Bigeye Tuna can be completed by examining its liver. The Bigeye Tuna has a grooved liver with clearly visible striations (fine lines looking like streaks), or dark blood vessels on the margins of the lobes. There are two lobes that are both of the same size. However in the yellowfin tuna these smooth lobes are devoid of these striations and the right lobe is clearly longer than the left lobe or the middle lobe. |