How to Identify Tuna

Obtain an identification guide to tuna. Comprehensive guidebooks cover every species and plenty of printable picture guides are available online. Laminate a printout if it is for a fishing trip.

Determine the geographical origin of the tuna. If you caught the fish yourself, this information is obvious. If the tuna is in a fish market, ask where it was caught. Be aware that the seller might not know for certain. The species of tuna will provide a clue as to its geographic origins as well. For example, black skipjack tuna are only found in the eastern Pacific Ocean and blackfin tuna inhabit the western Atlantic.

Measure the tuna. Some species are much bigger than others. While you can't rule out the fish being a juvenile of a large species, you can rule out any species whose maximum length is shorter than your specimen.

Note the coloring of the tuna. Most species have distinctive colors or markings. The blackfin tuna, for example, has a black stripe along its back that distinguishes it from similar species. Yellowfin tuna, as the name suggests, have bright yellow fins.

Examine the tuna's head, especially the relative size of the eyes and the angle of the mouth. Some of the clearest differences between tuna species appear in the face. The little tunny, for instance, has a protruding lower jaw.

Examine the tuna's fins and compare them to those of likely matches in the species guide. The shape, position and relative size of the fins varies from species to species.