Two samples of perch (Perca fluviatilis) older than 0+ juveniles, from two different ecosystems (River Danube and Lake Gruzansko jezero), were compared, based on 21 morphometric characters. The morphology during the studied periods of ontogeny was different in perch from the Danube and Lake Gruzansko jezero, probably as the result of differences in environmental conditions. This conclusion was corroborated by the different modes of morphological change between the various age classes.