In order to evaluate and compare the body shape of the bitterling (Rhodeus amarus) in Tajan, Babolroud, Siahroud rivers and Anzali lagoon using geometric - morphometric and traditional morphometric methods, 120 specimens were collected with electrofishing. To compare the traditional morphometric characteristics of the population, 29 morphometric characters were measured using digital caliper with 0.01 mm accuracy and 12 meristic characters were counted. Then to compare the geometric morphometric characters of the populations, left sides of the specimens were photographed using digital camera and 23 landmark points were digitized on 2D images using TpsDig2. The results were analyzed using MANOVA /CVA and PCA test. After the standardization of the measured characters using the PAST software, separating characters and their separation rate were determined via principal component analysis (PCA). For all the meristic factors of the studied populations, none have the coefficient factor above 0.8. Also, in morphometric characters for pre-anal length, head length and head height had coefficient factor above 0.8 in the first component. One-way ANOVA test results revealed that between all the characters, except for the characters scales of above lateral line anal and dorsal fin rays, body height, caudal peduncle length, predorsal length and length of anal fin, a significant difference was found between other characteristics (p<0.05). The results of geometric morphometric analysis showed partial difference in geometric forms between lagoon and river forms. But the comparison of morphometric and meristic features had shown a large overlap between the populations. This was to the extent that habitat conditions changes can be considered as a factor of population separation.