AquacuUure and Fisheries Management 1991, 22, 443-455 Electrophoretic analysis of protein variation in two Spanish populations of the European seabass, Dicentrarchus labrax L. (Pisces, Moronidae) G. MARTfNEZ Departamento de Genitica, Facultad de Ciencias, Universidad de Malaga, Malaga, Spain I. McEWEN & B. J. McANDREW Institute of Aquaculture, University of Stirling, Stirling, Scotland M. C. ALVAREZ Departamento de Genetica, Facultad de Ciencias, Universidad de Malaga, Malaga, Spain Abstract. One hundred specimens of the European seabass. Dicentrarchus labrax L., from a natural population (Cfidiz, Spain) were analysed by starch gel electrophoresis for 23 enzymes; 49 loci were identified, of whichfivewere polymorphic (/tD/yM/^r-J*, EST-3*, MEP-I* and SOD-2*) P = 10-2% and HQ = 1-8%. Twenty specimens from a hatchery at Tinamenor in northern Spain (Fl progeny from wild) were analysed for 28 different enzymes. A total of 61 loci were identified of which 4 were polymorphic {LDH-!', LDH-2', MEP-I' and XDH-2*) P = 6 6%.Ho= 1-5%. A total of 31 enzymesystemsand79differentloci were analysed in the two populations. The results suggest that the CSdiz and Tinamenor stocks are reproductively isolated and show a level of stock differentiation not previously known in populations of this species. An estimate of genetic distance based on the 31 loci compared in both populations gave a value of D = 0 012 ± 0 018 and a genetic similarity of I = 0-98S. The implications of these results forfisheriesand aquaculture are briefly discussed. Introduction Tlie European seabass, Dicentrarchus labrax L., is distributed in the north-eastern Atlantic Ocean and in the Mediterranean Sea (Tortonese 1986). It supports a very important commercial wildfisheryin both the Atlantic and the Mediterranean. In recent years seabass culture has been rapidly expanding in southern Europe and the Mediterranean area. Despite its importance there is relatively little published information on this species as a whole. There have been a number of fisheries studies in Irish and United Kingdom waters (Kennedy & Fitzmaurice 1972; Holden & Williams 1974; Pawson & Pickett 1987). The general biology of the species has been described by Barnabe (1980), its husbandry in captivity by Barnabe & Billard (1984) and its reproductive biology is covered in a number of papers (Brusle & Roblin 1984; Zohar, Billard & Weil 1984; Mayer, Shackley & Ryland 1988). The only published research on the genetics of this fish is a reference to its karyotype (Cataudella, Civitelli & Capanna 1973), an electrophoretic study of isoenzymes in a cultivated population in Italy (Cervelli 1985) and ontogenetic change in six isozymes (Basaglia, Salvatorelli, Santulli & D'Amelio 1989). Correspondence; Dr G. Martinez, Departamento de Genfitica, Facuitad de Ciencias, Universidad de MSlaga, Malaga 29071, Spain. 443