The Ponto-Caspian parasite Plagioporus cf. skrjabini reaches the River Rhine system in Central Europe: higher infestation in the native than in the introduced Danubian form of the gastropod Theodoxus fluviatilis

The introduction of non-indigenous organisms in new areas in the context of host-parasite interactions is still poorly understood. This study aimed at a parasitological and histopathological comparison of two phylogenetically distinct forms of the freshwater snail Theodoxus fluviatilis in the River Rhine system: the native Northern-European form, which showed a decline for unknown reasons and is nowadays extinct in the River Rhine, and the non-indigenous Danubian form, which was introduced via the Main-Danube canal. We histopathologically examined populations of Northern-European T. fluviatilis from three smaller rivers of the Rhine system and of Danubian T. fluviatilis from the River Rhine, after confirming the phylogenetic background of the respective population genetically. Results showed differences in the prevalence of trematodes and histopathologic organic alterations between the two snail forms. Both were infected with an opecoelid trematode Plagioporus cf. skrjabini, whereby its prevalence was significantly higher in the Northern-European than in the Danubian form. The parasitic trematode is, to our knowledge, a new trematode species in the River Rhine system, presumably co-introduced through the invasion of its second intermediate and final hosts, i.e. Ponto-Caspian amphipods and gobies. Its impact on native populations of Northern-European T. fluviatilis needs to be subject of future studies.

Automated summary

This study compared the parasitological and histopathological characteristics of two phylogenetically distinct forms of Theodoxus fluviatilis snail in the River Rhine system. Differences in prevalence of trematodes and organic alterations were observed between the native Northern-European form and the non-indigenous Danubian form, with the former showing higher prevalence of the opecoelid trematode Plagioporus cf. skrjabini. The presence of this new trematode species in the River Rhine system suggests a potential impact on native populations of Northern-European T. fluviatilis.