Water quality as a determinant of the composition of fish parasite communities

To investigate the relationship between fish parasite communities and water quality level, metazoan parasites were examined in 157 specimens of chub (Leuciscus cephalus L.), sampled in four lowland water courses (northern Italy): Ticino river (unpolluted), Naviglio Pavese Canal (slightly polluted), Lambro river near the Merone village (polluted) and near Monza (severely polluted). Dactylogyrus vistulae, Paradiplozoon ergensi, Bucephalus polymorphus, Acanthocephalus anguillae and larval stages of Tylodelphys clavata were found in all the sampled sites. The distribution of Lamproglena pulchella and Pomphorhynchus laevis was limited to the unpolluted and slightly polluted river sectors, while Asymphylodora tincae, glochidia, along with larval stages of Diplostomum spathaceum, were absent in the severely polluted site. The variability of the calculated infection indices (prevalence, mean abundance and mean intensity), the degree of interactivity among parasites, as well as parameters of species richness and diversity suggest that the structure of parasite communities are affected by the water contamination level.