In this study, data on trematodes of fishes from Lake Ladoga are reported. Thirty-nine parasite species of 12 families have been recorded. Among them, parasites of 6 families use fish as the intermediate host for the metacercariae stage. Trematodes of the other 6 families use fish as the definitive host. Fish acquired these parasites while feeding on benthic invertebrates (mollusks, aquatic insect larvae, leeches) and free-swimming cercariae.
Trematodes of 1 family infect fish both as maritae and as metacercariae. Data on the prevalence and abundance in all fishes are presented for each fluke species.