Salinity dependence of parasite infestation in the European eel Anguilla anguillain northern Germany

The aim of the study was to examine metazoan parasite communities of European eels (Anguilla anguilla) in fresh-water, brackish water and marine localities in northern Germany. In all, 29 parasite species/taxa were found in 170 eels: eight digeneans, one monogenean, five cestodes, ten nematodes, two acanthocephalans, and three crustaceans. Measures of diversity characteristics of the helminth communities included species richness, Shannon’s diversity index and its evenness, and the Berger–Parker dominance index. The highest species diversity and lowest dominance values were calculated for the helminth communities of eels from the two Baltic Sea localities. Parasite communities of European eels clearly exhibit the habitat preferences of their hosts, salinity-dependent specificities, and a clustering into fresh-water, brackish, and marine groups. The highly pathogenic parasite species Anguillicola crassus and Pseudodactylogyrus spp. were found at all sampling sites in fresh water and brackish water, with high prevalence. Basic information is provided on the risks of restocking programmes solely focusing on fresh-water sites.