Loss of microsatellite and mitochondrial DNA variation in hatchery strains of Japanese flounder Paralichthys olivaceus

Genetic divergence within and between hatchery strains and wild populations of Japanese flounder Paralichthys olivaceus was assessed by means of microsatellite and mitochondrial DNA (mtDNA) sequencing analysis. All of the 11 microsatellite loci screened in this study showed marked polymorphisms. Sequences of the mtDNA control region of Japanese flounder were also highly variable: of approximately 443 base pairs (bp) sequenced, 132 variable sites comprised of 149 base-substitutions were found among the 490 individuals. Marked reductions of genetic variability in the hatchery strains compared with the wild populations were observed in terms of number of both microsatellite alleles and mtDNA haplotypes, and mtDNA haplotype diversity. Both molecular markers yielded high values of F_ST (Φ_ST) between the hatchery strains, and between the hatchery strains and wild populations. We conclude that, based on the reduced genetic variability observed in all the hatchery strains examined, bottleneck effects occurred when each strain was founded.