Nine populations of the oyster Crassostrea gigas, were assayed for allozyme variation by starch gel electrophoresis. Three of the seven enzyme loci investigated are polymorphic: Lap, Mpi, and Pgi. Significant heterozygote deficiency was found in all seven Taiwan populations but not in the two populations of the Penghu Islands. Low levels of genetic variability (p = 0.14-0.42; H = 0.044-0.084) and little genetic differentiation (Nei's D < 0.01) were found among populations. Individuals with Lap heterozygotes were smaller than those with homozygotes in one population (p = 0.03) but this difference was statistically insignificant when adjusted significance level for multiple tests was used. Our results suggest that environmental factors may be important in determining regional differences in oyster size and shape.
Genetic variability, Heterozygosity
