• genetic structure;
  • electrophoresis;
  • allozyme;
  • Diplodus sargus;
  • Mediterranean Sea

An allozymic study was conducted on 190 individuals of white sea bream, Diplodus sargus sampled on five locations throughout the Lion's Gulf and the Ligurian Sea (Mediterranean Sea), in order to identify genetic structure. Electrophoretic surveys carried out on muscle and liver tissues identified 25 loci of which 12 were polymorphic (Pgeqslant R: gt-or-equal, slanted0.95). G-test analysis shows significant differences on allelic frequencies between the five stations at six loci. Examination of the spatial structure was performed using Nei's distances and F statistics, and indicated significant genetic differences between three groups. A group which clustered Blanes (Spain), Marseille (France) and Livorno (Italy) where the absence of genetic difference can be explained by migration of larvae and adults along a coastal ‘continuum’. The Elba sample (Italy) shows genetic divergence from other samples and this difference may result from isolation due to limited migration of larvae and adults. Banyuls (France), differs from all other stations. Several hypotheses are proposed to explain genetic patterns including local current systems, larval dispersal, geographic isolation and historical effects, and variation in the size classes of sampled individuals between sites.