Genetic characterization of wild and farmed European seabass in the Adriatic sea: assessment of farmed escapees using a Bayesian approach

Hybridizations between domesticated escaped farmed fish and wild conspecifics may increase genetic diversity or break down locally adapted gene complexes, thus reducing competitive ability and overall fitness. We examined the genetic structure of six farmed populations of European seabass, Dicentrarchus labrax, of different geographical origin, and ten neighbouring wild populations in the Adriatic Sea using 10 microsatellite loci. All loci were polymorphic, with mean expected heterozygosity > 74% in all 16 populations. Overall number of alleles as well as short-term effective population size were smaller in farmed (A = 18.7; N-e = 56.1) than in wild populations (A = 21.2; N-e = 180.6). The global FST of 0.0672 across loci showed significant population subdivision. Strong genetic differences between farmed fish and their wild conspecifics enabled the identification of seabass escapees back to their origins and the estimation of the extent of hybridization. Bayesian assignment analyses clustered wild populations together, whereas each farmed populations was assigned to a separate cluster. Intraspecific hybridization was highest in wild populations in areas impacted by fish farms, where highly admixed populations had decreased genetic diversity. The results of this study represent a solid foundation required to establish a genetic register of European seabass wild and farmed populations in the eastern Adriatic Sea that are required to establish a seabass DNA register.