Genetic variability and pedigree tracing of a hatchery-reared stock of red sea bream (Pagrus major) used for stock enhancement, based on microsatellite DNA markers

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 populations due to a reduced genetic variability of the released stock. This study compared the genetic diversity of a hatchery-reared stock of red sea bream (Pagrus major) used for stock enhancement with that of their broodstock. Its pedigree was also traced, using four to five microsatellite DNA markers, to quantify the actual number of reproducing parents. Then, the effective number of contributing parents (N-e) 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 (H-o = 0.856), was not significant different (P > 0.05) than that of the broodstock (H-o = 0.841). However, significant differences (P < 0.05) were found in the number of alleles per locus and in the frequencies among some major alleles of the two stocks. The pedigree of more than 73% of the progeny was effectively determined and at least 91 breeders tout of 250) actually reproduced. The estimated N-e was N-e = 63.7, consequently the estimated inbreeding coefficient was less than 0.8%. The results provide no evidence to consider a loss of genetic variation of the hatchery-reared stock, and a discussion on the possible effects of its release is presented. (C) 1999 Elsevier Science B.V. All rights reserved.