Unionid clams and the zebra mussels on their shells (Bivalvia: Unionidae, Dreissenidae) as hosts for trematodes in lakes of the Polish lowland

Abstract

The aim of this work was to determine the diversity and the prevalence of trematodes from subclasses Digenea and Aspidogastrea in native unionid clams (Unionidae) and in dreissenid mussels (Dreissenidae) residing on the surface of their shells. 914 individuals of unionids and 4,029 individuals of Dreissena polymorpha were collected in 2014 from 11 lakes of the Polish Lowland. The total percentage of infected Unionidae and Dreissenidae was 2.5% and 2.6%, respectively. In unionids, we found three species of trematodes: Rhipidocotyle campanula (Digenea: Bucephalidae), Phyllodistomum sp. (Digenea: Gorgoderidae) and Aspigdogaster conchicola (Aspidogastrea: Aspidogastridae). Their proportion in the pool of the infected unionids was 60.9%, 4.4% and 13.0%, respectively. We also found pre-patent invasions (sporocysts and undeveloped cercariae, 13.0%) and echinostome metacercariae (8.7%) (Digenea: Echinostomatidae). The majority of infected Dreissena polymorpha was invaded by echinostome metacercariae (98.1%) and only in a few cases we observed pre-patent invasions (bucephalid sporocysts, 1.9%). The results indicate that in most cases unionids played the role of the first intermediate hosts for digenetic trematodes or final hosts for aspidogastrean trematodes, while dreissenids were mainly the second intermediate hosts.