Parasites of genus Dactylogyrus exhibit a high species richness and high level of host specificity – majority of species show a preference for single host species or closely related host species. More than 900 described species emerged from high species richness of their hosts, which are freshwater fish of family Cyprinidae.

Dactylogyrus parasites were collected over two year period from cyprinid fish from 22 different localities over southern Balkan Peninsula. Of total 37 collected species of Dactylogyrus parasites from 36 cyprinid host species, 9 were identified as new for science. Other 27 species included endemic, highly host specific species, and commonly distributed Dactylogyrus species as well.

Molecular analyses based on combined sequences of partial 18S rDNA and ITS1 region revealed several complexes of cryptic species. Such examples are Dactylogyrus dyki parasitizing on cyprinids of Barbus genus, D. folkmanovae commonly found on Squalius and D. vistulae which represent generalist species parasitizing cyprinid species over several different genera. In the case of the last mentioned, molecular data showed not only variability between specimens collected from different host species, but also interpopulation variability between the specimens collected from Alburnoides thessalicus on two different localities.

Phylogenetic reconstruction revealed several lineages of Dactylogyrus parasites. Evolutionary and morphologically closely related Dactylogyrus species were found on Luciobarbus albanicus and Tropidophoxinellus helenicus representing two cyprinids with high evolutionary divergence. This may suggest recent host-switching of Dactylogyrus parasites between two phylogenetically non-related species living in the same geographical region i.e. species were collected in the same locality. Different case is D. rarissimus from cyprinids of Rutilus genus. This parasite species has been found on widely distributed R. rutilus in Europe and Balkan endemic R. haecklii as well. Dactylogyrus species similar to D. rarissimus on the base of morphological and molecular markers was also collected from Pelasgus laconicus and Telestes alfiensis. Nevertheless, these two endemic fish species do not live recently in parapatry with Rutilus, these foundings could suggest historical contacts of different cyprinid lineages.