Parasite assemblages of European bitterling (Rhodeus amarus), composition and effects of habitat type and host body size.

Parasite community composition of European bitterling (Rhodeus amarus), the only bitterling species occurring on the European continent, was investigated in 16 different localities from four European sea drainages during 1998-2007. A total of 41 species of metazoan parasites was identified. Nine parasite species are new records for European bitterling, namely Dactylogyrus rarissimus, D. suecicus, D. yinwenyingae, Gyrodactylus vimbi, Sphaerostomum globiporum, Petasiger sp., Paryphostomum radiatum, Ichthyocotylurus variegatus and Posthodiplostomum brevicaudatum. The specialist Gyrodactylus rhodei was the most widely distributed and one of the most prevalent species. The most frequent digenean species, represented by larval stages, was Metorchis xanthosomus. The parasite community of European bitterling was characterised by the dominance of generalists and parasites with autogenic life cycles. The rare occurrence of strictly endoparasitic species reflected the specific diet of the fish host. The character of the habitat significantly affected the parasite assemblages of bitterling. The greatest similarity was associated with lentic habitats (gravel pits and oxbows) and the lowest similarity between gravel pits and rivers. Juvenile bitterling from 8mm in length upwards were colonised by metazoan parasites, firstly by the monogenean G. rhodei. Host body size was positively correlated with parasite species richness, but the variability explained by length was low.