This study determined the composition of roach, Rutilus rutilus (L.), parasites in Lithuanian rivers. A total of 3558 individuals were examined for parasites from 12 rivers in 2005-2009. A total of 27 parasite species belonging to Ciliophora (6), Monogenea (3), Digenea (7), Cestoidea (4), Crustacea (3), Nematoda (1), Acanthocephala (1), Hirudinea (1), and Bivalvia (1) were recorded. Parasitological examinations of the roach showed significant variation in the prevalence of nine parasite species in the rivers studied. These results suggest that parasitological studies of specific parasite species in this freshwater fish can be used as bioindicators to provide information about environmental conditions in rivers.
