| Summary: | Fish parasites are an integral part of aquatic biodiversity sometimes ignored since they are often “hidden” in the hosts. Their interactions with other components of the ecosystem would be evaluated, especially when a parasite species is introduced in new areas and/or hosts. Human actions, including fish translocation for stocking, facilitate the parasites overcoming of biogeographic barriers and improve their dispersal ability. An example of human-aided circumvention of barriers, which contributes to homogenization of aquatic parasite fauna, is described. In 2010, the parasite Acanthocephalus rhinensis, previously found only in German Rhine River, was recorded in Piediluco Lake (Central Italy). In this new ecosystem, A. rhinensis, a heteroxenous parasite trophically-transmitted, uses eel Anguilla anguilla as definitive host (like in Rhine) and the amphipod Echinogammarus tibaldii as intermediate new host. Prevalence and abundance indicate that A. rhinensis population have found the conditions necessary not only for its survival but also for a firm establishment, dominating the eel intestinal community. The parasite don’t affect significantly eels health, but reduces the reproductive potential of E. tibaldii females. Considerations on how this parasite species has been introduced, the ecological factors which allowed a successful colonisation and the impact on host populations will be presented.
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