Morphology of the Genus Gymnocephalus (Pisces) from the Lower Danube River

The current study completed the information regarding the phenotypic variability in the Danube ruffe (Gymnocephalus baloni). We also assessed the phylogenetic relationship of G. baloni with the other two species of the genus Gymnocephalus from the Lower Danube River.

Ten morphological characters were the most useful together for discriminating between G. baloni and G. cernua from the Lower Danube River. In addition, we found a more streamlined body shape in G. baloni compared with the described holotype, which could be in connection with fish phenotypic response to ecological characteristics of the Lower Danube River.