Richness and diversity of parasite communities in European eels Anguilla anguilla Of the River Rhine, Germany, with special reference to helminth parasites

A total of 121 European eels (Anguilla anguilla) from 2 sampling sites on t he River Rhine were investigated in respect of their parasite communities. Special attention was given to the swim bladders, intestines, gills and fin s of the fish. Twelve different parasite species were found to live in and on the eels. Data from each sampling site were kept separate. Parasites fou nd in descending order of prevalence were: Anguillicola crassus, Trypanosom a granulosum, Myxobolus sp., Paratenuisentis ambiguus, Pseudodactylogyrus s p., Bothriocephalus claviceps, Myxidium giardi, Pomphorhynchus laevis , Tri chodina., Raphidascaris acus, Acanthocephalus lucii and Acanthocephalus ang uillae. Significantly different prevalences were reported for L-3 larvae of A. crassus, adult P. ambiguus, B. claviceps and Myxobolus sp. at the 2 sam pling sites. The highest number of parasite species was recorded from the i ntestine, which contained up to 6 different helminths. The coexistence of t he acanthocephalans P. laevis and P. ambiguus, which showed clear patterns of distribution within the intestine of the respective hosts, was reported for the first time. Up to 3 different helminth species were found in the in testine of individual fish. Among those, acanthocephalans were the most pre valent worms with the eel-specific parasite P. ambiguus as the dominant spe cies not only of the intestinal but also of the total component communities . Both infra and component communities exhibited low diversity and were dom inated by this single species. The evenness reached only approximately 50% or less and it remained unclear why the helminth communities of the eels fr om the River Rhine with its huge catchment area exhibit such a low parasite diversity and high dominance.