The black bream, Acanthopagrus butcheri, is an estuarine finfish found around the southern Australian coast including Tasmania. In Western Australia, this species inhabits rivers and estuaries as far north as the Murchison River south of Shark Bay Figure 1. It has supported a national commercial fishery of 200500 tonnes per annum, chiefly in Victoria Stuart and Grieve, 1993, and is a significant species in recreational and commercial fisheries in WA Anon., 1993. In WA black bream is considered to be a true estuarine species Potter et al., 1990 which means it spends its entire life cycle in the estuarine environment and only enters marine waters when it is flushed out of the estuary during extreme flooding Lenanton, 1976. Black bream in various localities are geographically isolated and may vary in features such as shape, lateral line, length of ventral fin and scale count. It is likely that a number of genetically discrete populations of black bream exist in Australia, especially as there is usually little movement of fish between estuaries Stuart and Grieve, 1993. All ten black bream populations studied in WA, using enzyme techniques, were genetically distinct Chaplin et al., 1998. Caution must therefore be applied when generalising about black bream populations specifically, spawning time varies between estuaries Stuart and Grieve, 1993; Sarre and Potter, 1999. Maximum sizes of 5360 cm total length and 3.54.0 kg has been reported in WA and Victoria respectively Stuart and Grieve, 1993; Chaplin et al., 1998 but differing growth rates have been reported from the many studies of wild populations around Australia Sarre, 1999; Tregonning et al., submitted. In the Swan River estuary they can reach a maximum age of over 21 years Sarre, 1999

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