The term “tuna” is widely used in commercial markets, referring to a diverse group of fish species spanning multiple biological classifications. This commercial ambiguity often makes it difficult for consumers to know exactly which fish they are purchasing. While many types of fish are marketed as tuna, the scientific definition is much narrower, distinguishing between true tunas and other related species.
The Scientific Classification of True Tuna
All fish known as tuna belong to the family Scombridae, which also includes mackerels and bonitos. Within this family, tuna are placed into the tribe Thunnini, encompassing approximately 15 distinct species across five different genera. These highly migratory fish share unique biological traits, such as the ability to regulate their body temperature above the surrounding water.
To be classified as a “True Tuna,” a species must belong exclusively to the genus Thunnus. This genus consists of eight species, making up slightly more than half of the Thunnini tribe. These eight species represent the most commercially recognized and valuable tunas found in the world’s oceans.
The Eight Species of True Tuna
The eight species within the genus Thunnus are categorized into two main groups: Bluefin and Yellowfin.
The Bluefin group includes the Atlantic Bluefin (T. thynnus), Pacific Bluefin (T. orientalis), and Southern Bluefin (T. maccoyii). These are the largest and most prized species globally. Atlantic Bluefin can exceed 10 feet in length and weigh over 1,000 pounds, and their rich, dark red, high-fat flesh is highly sought after for premium sushi and sashimi.
The Yellowfin group includes Yellowfin (T. albacares), Bigeye (T. obesus), Albacore (T. alalunga), Blackfin (T. atlanticus), and Longtail (T. tonggol). Yellowfin tuna, known as ahi in Hawaii, are recognizable by their distinct yellow finlets and are popular for grilling and searing due to their mild flavor and firm texture. Bigeye tuna are deep-water dwellers with large eyes and possess a higher fat content than Yellowfin, making them another popular choice for raw preparations like sashimi.
Albacore and Other Species
Albacore (T. alalunga) is the only species permitted to be labeled as “white meat tuna” in the United States. It is distinguished by its long pectoral fins and very light-colored flesh. While widely used in canned products, it is also consumed as steaks. The Blackfin tuna is a smaller species restricted to the western Atlantic Ocean, while the Longtail tuna is found in the Indo-Pacific region, often inhabiting coastal waters.
Species Commonly Sold as Tuna
The largest volume of fish sold under the general name “tuna” does not come from the Thunnus genus. The Skipjack tuna (Katsuwonus pelamis) is the single most common species caught and sold, making up more than half of the total global tuna catch. Skipjack is a member of the Thunnini tribe, but it is classified in its own genus, Katsuwonus.
Skipjack is the primary source for what is labeled as “canned light tuna.” It is a smaller, shorter-lived fish compared to the true tunas. Its flesh is darker and has a more pronounced flavor, which is why it is typically reserved for canning rather than fresh consumption. Other related species sometimes marketed as tuna include various types of Bonito, which belong to the genus Sarda.
Global Status and Sustainability Concerns
The intense global demand for tuna has placed significant fishing pressure on many stocks. The health of tuna populations is monitored closely by the International Seafood Sustainability Foundation (ISSF). According to recent data, approximately 65% of major commercial tuna stocks are at a healthy level of abundance, while 13% are categorized as overfished.
The health of individual species varies substantially. Skipjack stocks are considered robust and healthy due to their fast growth rate and widespread distribution. Conversely, all three Bluefin species remain a concern. Some regional stocks of Yellowfin and Bigeye, particularly in the Indian Ocean, are currently experiencing high levels of stress. These highly migratory species are managed by four major Regional Fisheries Management Organizations (RFMOs), which implement catch limits and conservation measures.