INFECTION OF EEL ANGUILLA-ANGUILLA (L) AND SMELT OSMERUS EPERLANUS (L) WITH ANGUILLICOLA-CRASSUS (NEMATODA, DRACUNCULOIDEA) IN THE NETHERLANDS FROM 1986 TO 1992

Dutch wild eels [Anguilla anguilla (L.)] and smelt [Osmerus eperlanus (L.)] from freshwater and saltwater areas in the Netherlands were coll ected from 1986 to 1992 and their swimbladders were examined for Angui llicola crassus (Nematoda, Dracunculoidea) and for parasite-related pa thological changes. Throughout the B-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 highe st prevalence between 1987 and 1988, and the highest intensity (i.e. n umber of parasites per infected fish) between 1988-1989. After 1989 th e prevalence of the parasite decreased, and the lesions became less se vere. Larger eels (23-34 cm) from the Waddenzee (salt water), which is close to the IJsselmeer, showed a high prevalence of the parasite fro m 1987 to 1990, although the intensity of infection decreased from 198 7 onwards, as did the percentage of fibrotic swimbladders after 1988. Smell, 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 p arasite shortly after 1988. Thereafter the prevalence stayed rather co nstant at about 40% of the smelt population. No pathological changes w ere found in the smelt.