Abstract
Several diagnostic genetic markers were identified in Pomatoschistus marmoratus and P. tortonesei using polyacrylamide gel electrophoresis (PAGE) of allozymes. Twenty‐one loci were resolved, including the electrophoretic pattern of muscle proteins. The MDH*, PGM‐,2*, EST‐1,2*, FUM* and PGI‐2* loci exhibited different alleles which were fixed for the two species being analysed. Genetic distance, as calculated by Nei's index, showed a value of 0·413. Environmental hypersalinity, could have influenced the geographical distribution of P. tortonesei .