Degree of differentiation among populations of twaite shad, Alosa fallax nilotica, in Turkish territorial waters was evaluated with the truss morphometric system using Discriminant Function (DFA) and Principal Component Analyses (PCA). Approximately 40 individuals were collected from each sea to represent regions. In DFA, the proportion of correctly classified Eastern Mediterranean sea sample to their original group was highest (90 %) with a high overall random assignment of individuals into their original population (78 %). Plotting discriminant function 1 (DF1) and discriminant function 2 (DF2) explained 100 % of total between group variability and clearly discriminated Eastern Mediterranean sea sample from the Baltic and Aegean sea samples, which were over plotted. This findings was also supported in multivariate analysis of variance. PCA revealed that the observed differences were mainly from posterior morphometric measurements of the fish. The patterns of morphological differentiation suggested that there is limited exchange of individuals among areas to homogenize populations phenotypically from the Black and Aegean seas to Eastern Mediterranean sea.
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