Acheilognathidae

4.1 | Acheilognathidae

Based on morphological characters, Rhodeus colchicus was described from the River Natanebi in the Georgian Black Sea basin ( Bogutskaya & Komlev, 2001) and the species is widespread from the North Caucasus to the south, not reaching Turkey. Molecular studies ( Bartáková et al., 2019; Bohlen, Šlechtová, Bogutskaya, & Freyhof, 2006) revealed that R. colchicus is nested within Rhodeus amarus . In their phylogenetic analysis, Bartáková et al. (2019) found six different molecular groups of bitterlings in the western Palearctic, R. colchicus representing one of these. The phylogenetic structure of these six clades is poorly supported in the analysis by Bartáková et al. (2019) and it cannot be excluded, that R. colchicus might be the sister group of all other western Palearctic bitterling clades. Similar results have been obtained earlier by the study done by Bohlen et al. (2006). Geiger et al. (2014) suggest that lineages of European bitterlings are very closely related and might be better considered as a separate populations rather than species. However, as the consensus of species status of R. colchicus is not yet reached, we keep R. colchicus as a separate species in the presented list.