Morphological variation of Lithognathus mormyrus (Linnaeus, 1758) samples harvested in six Mediterranean lagoons was investigated using 23 truss elements and 11 conventional linear measurements. Multivariate analyses revealed a highly significant morphological discrimination between western Mediterranean basin samples (lagoons of Bizerta, Ghar El Melh and Mellah) that differ from each other but are also differentiated from the oriental lagoon samples (lagoons of El Biban, Farwa and Venice) by some variables, which are related to the head length. Thus, our findings highlighted the peculiarity of the Mellah lagoon specimens (Algeria), which have the smallest heads compared to the other samples. This morphological variation seems to be associated to various constraints represented by the feeding strategy, and availability, type and size of ingested prey. As for the oriental specimens, they tended to cluster. However, significant differences, related to the caudal peduncle length, were detected, especially between El Biban specimens and those of Farwa and Venice lagoons. This morphological variation appears to be primarily associated to hydrodynamic constraints. The morphological divergence among the various studied samples is suggested to be environmentally-induced (phenotypic plasticity).