There is not one individual fish called “tuna” – there are more than a dozen species of tuna worldwide. Many tuna companies, in fact, now track and label their canned tuna products to identify the specific type of tuna, the ocean where it was caught, and more.
We’re highlighting the seven major commercial tuna species on this page, six in the genus Thunnus and one in the genus Katsuwonus. “Minor” or less economically important tunas, not covered here, include bullet tuna, blackfin tuna, and tonggol.
Tuna species share some distinctive characteristics. For instance, due to the physiology of their respiratory system, tunas are obligate ram ventilators — that is, they need to swim constantly to make water pass through their gills. Because they swim constantly to oxygenate their blood, their muscular metabolism continuously generates heat, which gives them a unique feature among all bony fishes — the ability to regulate their body temperatures. Their thermoregulation capacity enables them to tolerate a wide range of water temperatures.
Consequently, tuna are highly migratory: they are widely distributed throughout all oceans in the world between equatorial and subpolar latitudes of both hemispheres. However, some tuna stocks are more abundant — or less heavily fished — than others. To learn about the status and sustainability considerations for each tuna species below, read our Status of the Stocks report.