This study was conducted to determine the body shape variation among the populations of the Crested loach, genus Paracobitis, in the southeast Caspian Sea basin using landmark-based geometric morphometrics. In this research, 113 fish samples from Paracobitis genus were sampled from the Tajan,
Babolrood, Atrak, Gorganrood rivers in summer using electroshocker. Then, the left sides of the fish samples were photographed by a digital camera. Fifteen landmark-points were digitized on twodimensional images using TpsDig2 software. The obtained results from Landmark data were analyzed and multivariate statistical analyses such as PCA, CVA and cluster analysis (CA) were used and eventually, the Phenotype plasticity patterns of each population related to the shape of overall average of populations were illustrated. The results demonstrated that there was a significant difference among the four studied populations in terms of morphological features (P<0/0001). The conclusions of the present study can improve understanding of growing phenotype patterns plasticity of these fishes in the water bodies of different river systems from the southeast basin of the Caspian Sea as well as of identifying species of Paracobitis populations in the Tajan and Babolrood  rivers.