Molecular tools in a marine restocking program for the endangered dusky grouper, Epinephelus marginatus

The dusky grouper (Epinephelus marginatus) is an endangered marine fish for which a restocking program has been undertaken in the Mediterranean Sea. Genetic variation at six microsatellite loci was assayed to help plan preservation of genetic diversity after release of hatchery-reared juveniles. We estimated relatedness and effective population size within two groups of captive broodstock, assessed genetic variability of these broodstock and F1 juveniles compared to natural populations, and investigated genetic relationships between hatchery-reared and wild specimens inhabiting the release site. On average, no relatedness was found within captive broodstock and a potentially high number of effective breeders was assessed (N-b D 86.9; CI 95% D 46.0-451.2). However, very few breeders (N D 7) spawned successfully, and a positive degree of relatedness (r(W) D 0.0297) was found among this particular subset of individuals. Genetic variability parameters were reduced for the broodstock and F1 juveniles, although not significantly. Genetic differentiation was detected among released juveniles and wild conspecifics collected 75 km away from the target area. However, the pattern of genetic distances from other wild populations justifies the choice of the broodstock as the best alternative donor stock.