Clinal variations of discriminative meristic characters of sea bass, Dicentrarchus labrax (Moronidae, Perciformes) populations on Tunisian coasts
Morphological variation of eight groups of samples (317 individuals) of Mediterranean Sea bass, Dicentrarchus labrax (Linnaeus, 1758) collected throughout northern and eastern-south Tunisian coasts was investigated using seven meristic characters. Tunisian coasts are important to study as they are considered as a transitional area between western and eastern Mediterranean basins. Average comparisons and Discriminant Function Analysis showed, for two characters, the number of lateral line scales and gillrakers number, clusters allowing the distinction between samples collected in the eastern Mediterranean basin and those caught in the western basin. The comparison of the averages for these two characters with those reported in other geographical locations (Atlantic: Morocco; Golfe du Lion, Annaba and Gulf of Gabès) highlights a decreasing cline for the number of gillrakers and an increasing one for the number of lateral line scales, from the Atlantic Ocean to the western basin of the Mediterranean and then to the Eastern basin. These results suggest that the variation of these two meristic characters is related to the gradual evolution of physicochemical characteristics in these transitional areas. Moreover, these findings seem to be consistent with the existing pattern of genetic differentiation in this area.