Biological and Genetic Characteristics of Restocked and Wild Acanthopagrus butcheri (Sparidae) in a Southwestern Australian Estuary

Abstract

Acanthopagrus butcheri was restocked in an estuary in which it had become depleted. The restocked fish were cultured in 2001 and 2002 using broodstock from that estuary. These fish, whose otoliths had been stained with alizarin complexone, were released into the estuary and their biological performance tracked for seven to eight years. The 2002 cohort, introduced at circa four months old in autumn, survived far better than the 2001 cohort, introduced at circa seven months old in winter, when freshwater discharge peaks and temperatures are low. While restocked fish matured and grew nearly as fast as wild fish, the increase in density was accompanied by a reduced growth of wild fish. Genetic comparisons, using seven microsatellite loci, demonstrated that the expected heterozygosity and relatedness of restocked and wild A. butcheri, which is naturally characterized by low levels of genetic polymorphism, were similar. Although culturing did not demonstrably increase the level of inbreeding, it did result in the loss of some rare alleles. The biological and genetic results, together with the contribution of restocked A. butcheri to the commercial catch for this species in the estuary rising to 62–74% by 2007–2010, demonstrates the efficacy of using restocking to replenish depleted A. butcheri stocks.

Keywords:

• cultured fish
• growth
• maturity
• density-dependent effects
• genetic diversity
• contribution to fishery

ACKNOWLEDGMENTS

The authors’ gratitude is expressed to Trevor Price for providing samples of his commercial catch and sharing his knowledge of black bream; to Vanessa Forbes (Department of Water, Western Australia) for information concerning water quality in the Blackwood River Estuary; and to the staff and students of the Centre for Fish and Fisheries Research, Western Australian State Agricultural Biotechnology Centre and Challenger Institute of Technology, who helped with sampling and culturing black bream and in the operation of the ABI 3730 DNA Analyzer. The Department of Fisheries, Western Australia, the West Australian Fish Foundation, the Australian Fisheries Research and Development Corporation and Murdoch University provided financial support. Two anonymous referees are also thanked for their constructive criticisms.