Ophthalmohelminthiasis of Perca fluviatilis L. (Actinopterygii: Perciformes) in the middle reaches of the Saratov reservoir

The infestation of river perch Perca fluviatilis of opthalmic parasites in the middle reaches of the Saratov reservoir in 2013-2016, 2018, 2020 was studied. Four species of helminths have been registered: the nematode Desmidocercella spр. and the trematodes Diplostomum spathaceum, Posthodiplostomum brevicaudatum, Tylodelphys clavata, for which P. fluviatilis serves as an intermediate host. All detected trematode species are pathogens of fish diseases. In most cases, P. fluviatilis invasion occurs in the form of asymptomatic parasite carriage. An analysis of the long-term dynamics of P. fluviatilis infestation showed significant fluctuations in the parasite prevalence and a change in the dominant species in the group of macroparasites localized in the eyes of perch. The results obtained may indicate some instability of parasitic systems involving these parasite species and P. fluviatilis in the studied area of the reservoir.