New Data on Endohelminth Communities of Barbel from the Bulgarian Part of the River Danube.

Species diversity and composition of the parasite communities of barbel () at the infracommunity and component community levels were studied in the Lower Danube River, Bulgaria. During the two-year investigations, five parasite species have been found in 92 host fish: (Cestoda), and (Acanthocephala) and larval stages of sp. and (Nematoda). and found in barbel represented new host records in Bulgaria. Parasite communities of barbel were species-poor and highly unbalanced. represented the dominant (core) species (prevalence 98.9 %), the second most frequent component parasite was sp. (P = 14.1 %) and remaining three species occurred only accidentally in barbels. Differences in species richness, prevalence, intensity of infection and ecological indices between individual seasons (spring, summer, autumn) were statistically signifi cant, but considerably affected by unequal species structure of communities with highly prevailing . Low parasite species diversity of barbel and low values of most ecological indices, when compared with previous studies in this area (or other Bulgarian parts of the River Danube) might indicate that environmental conditions are impaired and thus, not favourable for the development of barbel parasites (primarily to their intermediate host survival) in the Lower Danube River of Bulgaria.