Additional Observations on the Biology of the Northern Bluefin Tuna, Kishinoella tonggol (Bleeker), in Australia

Abstract

The northern bluefin tuna, Kishinoella tonggol (Bleeker), occurs along the whole of the north coast of Australia and on the east and west coasts as far south as Twofold Bay, N.S.W., and Cockburn Sound, W.A., respectively. Fin formulae, scale row and gill-raker data, and morphometrical characters are recorded separately for fish of the northern, eastern, and western regions. Marked regional differences occur; but it is considered that these can be largely (though not entirely) explained by differential growth of body parts, since only small sizes are found in the extreme north whereas large sizes predominate in the southern portions of the range. The hypothesis of two distinct species, suggested by size group distribution and regional variations, is rejected. Sexual maturity in K. tonggol is reached in the third year of life and spawning is in the summer. The species apparently feeds mainly on pelagic organisms.