|
Figure 1 : Map showing distribution of Black Bream in Australia
|
|
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 200-500 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 Distribution
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 53-60 cm total length and 3.5-4.0 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).
Very efficient hatchery technology has been developed for this species by the Fremantle Maritime Centre (FMC) and this has allowed trial stocking in the Swan (Lenanton et al., 1999) and Canning Rivers and in man-made marinas in Perth (Jenkins et al., 1999). Commercial production of fingerlings has led to the stocking of many private dams and a major study of the survival of black bream in such dams was recently completed (Sarre, in prep.). There is also interest in commercial aquaculture of this robust, high quality table fish, particularly in Victoria. Sea cage trials have been undertaken at Jurien in Western Australia and large black bream have been stocked into commercial facilities where fishers pay for the privilege of fishing for this species.
Culture Environment
The black bream is a euryhaline species, which means it can tolerate a wide range of salinities. Black bream may be found in salinities ranging from less than 3 parts per thousand (ppt) to those exceeding that of sea water (more than 35 ppt) (Sarre, 1999) and under experimental conditions high survival and significant growth has been achieved up to 60 ppt (Jenkins et al., 1999).
Survival of black bream in freshwater dams (<1ppt) has been very poor, especially during winter, although tolerance of low salinity may increase with fish size (Weng, 1971). In captivity, black bream are reported to have tolerated water temperatures from 8-33 o C, although it is unlikely that these extremes could be withstood for any period of time (Tregonning et al., submitted).
Informtation courtesy of the WA Department of Fisheries 
|
