The southern bluefin tuna, Thunnus maccoyii, is a tuna of the family Scombridae found in open southern Hemisphere waters of all the world's oceans mainly between 30°S and 50°S, to nearly 60°S.
At up to 2.5 metres (8.2ft) and weighing up to 260 kilograms (570lb), it is among the larger bony fishes.