Tuna is a globally valued fish, enjoyed in various culinary traditions. Its widespread presence often leads to questions about its diversity. Understanding the different types of tuna can be complex, as the term “tuna” is sometimes used broadly. This article clarifies what defines a true tuna and explores its various species.
What Makes a Tuna a Tuna?
True tunas belong to the genus Thunnus, which is part of the larger mackerel family, Scombridae. These fish possess several distinctive biological features. They are known for their streamlined, torpedo-shaped bodies, adapted for rapid, efficient movement through water. Their coloration typically features dark blue to black on the dorsal side and shimmering silver to white on the ventral side, providing camouflage in the open ocean.
A unique characteristic of true tunas is their ability to regulate body temperature, making them endothermic. This allows them to maintain a higher body temperature than the surrounding water, enabling sustained high-speed swimming and deeper dives into colder waters. Tunas are also obligate ram ventilators, meaning they must continuously swim with their mouths open to force water over their gills for oxygen uptake. This constant motion contributes to their muscular physique and migratory patterns across vast ocean expanses.
The Principal Tuna Species
The genus Thunnus comprises eight distinct species, divided into two subgenera reflecting their evolutionary relationships. The bluefin group includes the Atlantic bluefin tuna (Thunnus thynnus), known for its large size and extensive migrations across the Atlantic, and the Pacific bluefin tuna (Thunnus orientalis), a prized species of the North Pacific. The Southern bluefin tuna (Thunnus maccoyii) completes this group, inhabiting the southern oceans.
The yellowfin group features the yellowfin tuna (Thunnus albacares), distinguishable by its bright yellow finlets and widespread distribution in tropical and subtropical seas. The albacore tuna (Thunnus alalunga) is recognized by its exceptionally long pectoral fins and lighter-colored flesh. The bigeye tuna (Thunnus obesus) is another prominent species, often confused with yellowfin but typically having larger eyes and a more robust body.
Rounding out the true tunas are the blackfin tuna (Thunnus atlanticus), found in the western Atlantic, and the longtail tuna (Thunnus tonggol), prevalent in the Indo-West Pacific.
Relatives in the Scombridae Family
While the term “tuna” often specifically refers to species within the Thunnus genus, the broader Scombridae family encompasses many other related fish. This family, which includes mackerels and bonitos, contains 51 species across 15 genera. True tunas are just one part of the Thunnini tribe, which itself consists of five genera.
Other members of the Scombridae family are sometimes colloquially called tuna due to shared characteristics like streamlined bodies and open-ocean habitats. For example, the skipjack tuna (Katsuwonus pelamis) is a commercially important species that belongs to a different genus within the Thunnini tribe. Various species of bonito (Sarda spp.) and mackerel are also part of this family but are not classified as true tunas.
Other Scombridae family members include:
- Wahoo (Acanthocybium solandri)
- Bullet tuna (Auxis rochei)
- Frigate tuna (Auxis thazard)
- Kawakawa (Euthynnus affinis)
- Little tunny (Euthynnus alletteratus)
These relatives share some common traits with true tunas, such as being fast swimmers and predators, but they differ in aspects like body shape, fin structure, or dentition.
The State of Tuna Populations
The global health of tuna populations is a concern due to their commercial importance and migratory nature. As of March 2025, the International Seafood Sustainability Foundation reported that 65% of the 23 major commercial tuna stocks were at healthy levels, while 26% were at an intermediate level and 9% were overfished. Overfishing remains a primary threat, compounded by factors such as habitat degradation and climate change.
Despite challenges, conservation efforts show positive results for certain species. In 2021, Atlantic bluefin tuna improved its status from Endangered to Least Concern on the IUCN Red List, and Southern bluefin tuna moved from Critically Endangered to Endangered. Albacore and yellowfin tunas also improved from Near Threatened to Least Concern. However, some populations, like Pacific bluefin tuna, remain severely depleted, with less than 5% of their original biomass. These varying statuses highlight the need for continued monitoring and international management to ensure long-term sustainability.