The pattern of morphometric differentiation among six populations of Clarias gariepinus sited in the Asi, Seyhan, Ceyhan, Goksu, Aksu, and Sakarya river systems in Turkey was examined. Univariate analysis of variance revealed significant differences between means of the six samples for 18 out of 20 standardized morphometric measurements. The first canonical function accounted for 39 % and the second for 29 % of between-group variability. In principal component analysis, the first component accounted for 20 % and the second for 12 % of the shape variations among the samples. Plotting the first and second principal components showed that the observed differences were mainly from measurements taken from the head of fish, indicating this region to be important in the description of population characteristics. Visual examination of the samples along the canonical functions revealed a clear between-sample differentiation. All the samples except the Seyhan and Aksu samples were clearly distinct from each other. Sakarya and Goksu samples were mostly isolated from each other and from all other samples. The overall random assignment of individuals into their original groups was high (78%). The proportion of correctly classified individuals into their original group was highest in the Sakarya sample (93%) and high in the Goksu (89 %) and the Ceyhan (86 %) samples, indicating that these samples are highly divergent from each other.