Genetic variation of wild and hatchery populations of the Pacific oyster, Crassostrea gigas (Thunberg), in Australia

Pacific oysters were introduced to Tasmania about 50 years ago from Japan; fears had been expressed that they would have lost genetic variation during their subsequent naturalisation. Using 17 allozyme loci, three hatchery an d four naturalised populations of Crassostrea gigas (Thunberg) in Australia were compared with one another and with two endemic Japanese populations. All populations showed a high degree of genetic variability. The percent of polymorphic loci ranged from an average of 70.6% (hatcheries) through 73.5 % (naturalised and Japan). Mean observed heterozygosities ranged from 0.267 (naturalised) through 0.285 (hatcheries) to 0.291 (Japan). Mean numbers of alleles per locus ranged from 3.0 (hatcheries) through 3.3 (naturalised) t o 3.5 (Japan). Most loci and populations showed good fits to Hardy-Weinberg expectations; the few significant exceptions were heterozygote deficiencie s. Allele-frequency differences among populations were minor, although some times statistically significant: only about 1% of the allele frequency vari ation could be attributed to among-population differences. The introduced o ysters appear to have retained most of the genetic variation present in the Japanese populations. (C) 2000 Elsevier Science B.V. All rights reserved.