Studies on genetic variability of hatchery and wild populations of fishes by DNA markers

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Stock enhancement programs that use a small number of breeders for the production of hatchery-reared juveniles to be released to the environment, may have negative effects on the genetic diversity of wild popurations due to a reduced genetic variability of the released stock. In this study, genetic diversity of wild and hatchery population of red sea bream (Pagrus major) was surveyed using DNA molymorphic markers to monitor genetic change in the brood stock and hatchery reared population. Five primer sets for PCR amplification were constructed for the microsatellite loci and the loci charcterized by screening polymorphism in red sea bream. The genetic variability was evaluated by average numbers of alleles per locus and mean heterozygosity. Distinct genetic changes in the hatchery populations were observed mainly in the average numbers of alleles per locus, but not in mean heterozygosity. This suggested that these genetic changes were mainly caused by bottle-neck effects and not by inb … More reeding. Brood stock and its pedigree were also traced, using five microsatellite DNA markers, to quantify the actual number of reproducing parents. Then, the effective number of contributing parents (Ne) and the inbreeding coefficient were estimated. It was found that the genetic diversity of the hatchery-reared stock in terms of the mean observed heterozygosity (Ho=0.856), was not significantly different (p>0.05) from that of the broodstock (Ho=0.841). However, significant differences (p<0.05) were found in the number of alleles per locus and in the frequencies of some major alleles between the two stocks. The pedigree of more than 73.5% of the progeny was effectively determined and at least 91 breeders (out of 250) actually reproduced. The estimated Ne was 63.7, consequently the estimated inbreeding coefficient was less than 0.78%. A way to conserve genetic variability and to prevent a loss of genetic variation in the hatchery-reared stock, were discussed and proposed based on the evidence obtained in this study. Less