Allozyme variation and stock structure in the black bream, Acanthopagrus butcheri (Munro) (Sparidae) in southern Australia: implications for fisheries management, aquaculture and taxonomic relationship with Acanthopagrus australis (Gunther)

An investigation of allozyme variation at 32 loci in the black bream, Acant hopagrus butcheri (Munro), and the yellowfin bream, Acanthopagrus australis (Gunther), revealed heterozygosities (H) equal to 0.035 and 0.065, respect ively, and polymorphism (P-0.95) equal to 0.067 and 0.200, respectively. Th e genetic data confirm the very high level of genetic similarity previously found between the two species, but nevertheless also support their recogni tion as separate species. The finding of only limited allozyme differentiat ion at three polymorphic loci amongst six black bream samples from south-ea stern Australia is consistent with the existence of a single panmictic popu lation in this region. This would require that adult black bream have a gre ater capacity to survive in near-shore marine environments than previously realised and that dispersal between estuaries is more extensive than was sh own by tagging studies. In contrast, significant differences were found at two loci between black bream from south-eastern Australia and a sample from south-western Australia. The degree of genetic divergence between stocks i n south-eastern and south-western Australia suggests that only local brood stock should be used for aquaculture or re-stocking as a precaution until f urther investigations with DNA-based techniques are conducted. The genetic divergence detected supports separate management for populations in Western Australia and Victoria.