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 and 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) to 3.5 (Japan). Most loci and populations showed good fits to Hardy-Weinberg expectations; the few significant exceptions were heterozygote deficiencies. Allele-frequency differences among populations were minor, although sometimes statistically significant: only about 1% of the allele frequency variation could be attributed to among-population differences. The introduced oysters appear to have retained most of the genetic variation present in the Japanese populations. (C) 2000 Elsevier Science B.V. All rights reserved.