Contribution assessment of hatchery origin black sea bream Acanthopagrus schlegeli into natural populations using microsatellite markers

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Genetic diversity of hatchery origin black sea bream (Acanthopagrus schlegeli) released at Daio Bay in Japan was monitored during two consecutive years using 6 microsatellite DNA markers. The number of alleles per locus ranged from 6 to 20 while Ho averaged 0.83-0.88 at all loci. Departures from HWE were observed in all samples, showing heterozygosity excess in both offspring groups and deficit in the broodstock and wild samples. The 33.7% and 38.5% of the specimens in 2003 and 2004, respectively ; were identified as hatchery origin, with another 40% of the samples matching with a single parent each year, suggesting admixture with the natural population. The offspring groups presented a reduction of 28.9% of the alleles regarding the broodstock for the two years analyzed. The homogeneity between groups was also confirmed by the low values of Fst, warning about the necessity of monitoring the genetic diversity of black sea bream inhabiting Daio Bay during longer periods in order to avoid possible genetic drifts. The results obtained in the present study represent a clear example of how despite the high survival rates of previously released juveniles ; mating small number of breeders may unleash negative impact on genetic diversity. This experience evidences the necessity of estimating and monitoring the genetic evolution on natural resources whenever stock enhancement practices are carried out.