Molecular and morphological description of <i>Diplostomum spathaceum</i> metacercariae from <i>Abramis brama</i> l. Of Lake Syamozero (North-West Russia)

Trematodes Diplostomum von Nordmann, 1832 are widely distributed parasites with complex life cycles involving freshwater snails as the first intermediate hosts, various fish species as the second intermediate hosts, and fish-eating birds as definitive hosts. Metacercariae of Diplostomum spp. are important fish pathogens with problematic morphological identification. The present research of Diplostomum larvae in the eyes of the freshwater bream Abramis brama was carried out within the framework of the long-term parasitological monitoring of fish in Lake Syamozero. The study has provided molecular and morphological characterization of Diplostomum spathaceum metacercariae from the lens of the freshwater bream. The partial cox1 mtDNA sequences used for molecular identification of the isolates were identical with those obtained previously, but morphological features of the metacercariae matched the literature data only in part. Comparison of different dimensions of parasites by discriminant analysis suggests that Diplostomum rutili is a junior synonym of Diplostomum spathaceum. New and archival data on diplostomids from bream’s eyes demonstrate a long-term increase in the infection prevalence.