Thunnus maccoyii, commonly known as the southern bluefin tuna, is a large, highly migratory pelagic fish in the family Scombridae. It is native to the temperate and cold waters of the Southern Hemisphere, particularly the southern Indian Ocean, the Tasman Sea, and waters off southern Australia, New Zealand, and South Africa. The genus name Thunnus derives from the Greek thýnnos, meaning “tuna” and the species epithet maccoyii honors Frederick McCoy, a 19th-century Irish-Australian naturalist. The common name “southern bluefin tuna” distinguishes it geographically from the Atlantic bluefin (Thunnus thynnus) and the Pacific bluefin (Thunnus orientalis).

Historically, southern bluefin tuna was harvested by coastal communities in Australia and Japan, but in the 20th century it became a major international commercial species, especially for export to Japan for raw consumption. Today it is heavily regulated due to significant population declines from overfishing. As a food source, Thunnus maccoyii is prized for its high lipid content and richly marbled flesh, making it especially valued for sashimi and sushi. Like other bluefin species, it is divided into cuts based on fat distribution, including lean akami and fatty toro sections. In Japan, it is considered one of the most premium tuna species for raw consumption, while in Australia it has also been consumed grilled or seared. Modern production includes both wild capture and tuna ranching, particularly in South Australia, where juveniles are captured and fattened in sea pens before export. It is primarily associated with Japanese cuisine in its highest-value culinary form, though it is also part of contemporary Australian and global seafood gastronomy.

Thunnus maccoyii contains omega-3 fatty acids, particularly eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), vitamin D (cholecalciferol), vitamin B12 (cobalamin), selenium and taurine. As a long-lived apex predator, it can bioaccumulate methylmercury, a heat-stable neurotoxic compound formed in marine ecosystems, which poses health considerations with frequent or high-level consumption. The balance between nutritional benefits and contaminant risk has made southern bluefin tuna both a highly valued and carefully managed food source in modern ethnobiological and regulatory contexts.