GENETIC DIFFERENTIATION OF WHITE SEA BREAM WITHIN THE LIONS GULF AND THE LIGURIAN SEA (MEDITERRANEAN-SEA)

An allozymic study was conducted on 190 individuals of white sea bream , Diplodus sargus, sampled on five locations throughout the Lion's Gul f and the Ligurian Sea (Mediterranean Sea), in order to identify genet ic structure. Electrophoretic surveys carried out on muscle and liver tissues identified 25 loci of which 12 were polymorphic (P less than o r equal to 0.95). G-test analysis shows significant differences on all elic frequencies between the five stations at six loci. Examination of the spatial structure was performed using Nei's distances and P stati stics, and indicated significant genetic differences between three gro ups. A group which clustered Blanes (Spain), Marseille (France) and Li vorno (Italy) where the absence of genetic difference can be explained by migration of larvae and adults along a coastal 'continuum'. The El ba sample (Italy) shows genetic divergence from other samples and this difference may result from isolation due to limited migration of larv ae and adults. Banyuls (France), differs from air other stations. Seve ral hypotheses are proposed to explain genetic patterns including loca l current, systems, larval dispersal, geographic isolation and histori cal effects, and variation in the size classes of sampled individuals between sites. (C) 1996 The Fisheries Society of the British Isles