Dutch wild eels [Anguilla anguilla (L.)] and smelt [Osmerus eperlanus (L.)] from freshwater and saltwater areas in the Netherlands were collected from 1986 to 1992 and their swimbladders were examined for Anguillicola crassus (Nematoda, Dracunculoidea) and for parasite-related pathological changes. Throughout the 6-year sampling period, young eels (up to 17 cm) showed severe pathological changes due to the parasite. The prevalence of infection in larger eels (23-34 cm) showed the highest prevalence between 1987 and 1988, and the highest intensity (i.e. number of parasites per infected fish) between 1988-1989. After 1989 the prevalence of the parasite decreased, and the lesions became less severe. Larger eels (23-34 cm) from the Waddenzee (salt water), which is close to the IJsselmeer, showed a high prevalence of the parasite from 1987 to 1990, although the intensity of infection decreased from 1987 onwards, as did the percentage of fibrotic swimbladders after 1988. Smelt, which is a paratenic host for larvae of A. crassus and which is a prey for large eels, showed a sharp decrease in prevalence of the parasite shortly after 1988. Thereafter the prevalence stayed rather constant at about 40% of the smelt population. No pathological changes were found in the smelt. |
