Eel parasite diversity and intermediate host abundance in the River Rhine,Germany

European eels (Anguilla anguilla) from 2 sampling sites on the Rhine river (near Karlsruhe and near Worms) were investigated with respect to their par asite communities. Nine different metazoan species were found to live in an d on the eels. The highest number of species was recorded from the intestin e, which contained up to 6 different helminths. Among these, acanthocephala ns were the most prevalent worms with the eel-specific parasite Paratenuise ntis ambiguus as the dominant species of the intestinal component communiti es at both sites. Comparing the intestinal parasites from eels caught near Karlsruhe with those from Worms, the acanthocephalans showed a significantl y lower abundance at Worms. A significantly lower mean number of intestinal helminth species as well as a significantly lower Brillouin's Index was fo und at Worms compared,vith Karlsruhe. This difference could be related to t he abundance of the respective intermediate crustacean hosts. At the sampli ng site Worms the amphipod Corophium curvispimon was the dominant crustacea n. Additionally, only the isopod Jaera istri and the amphipod Dikerogammaru s villosus were found. All these crustacean species have only recently colo nized the Rhine river system via the Main-Danube canal, built in the early 1990s. They are not known to act as intermediate hosts for any of the acant hocephalans found in the eels. The site near Karlsruhe exhibited a higher c rustacean diversity, including Asellus aquaticus and different species of t he genus Gammarus, which are all known intermediate hosts for the acanthoce phalans found. Therefore, changes of eel parasite diversity can be correlat ed with the appearance of invading crustacean species (neozoans).