Abstract
The aim of the study was to determine the prevalence and intensity of infection of European eel, Anguilla anguilla (L.), with nematode and monogenean gill parasites. Fifty individuals obtained from Vistula Lagoon stocking material were examined in August and October 2006. The prevalence of infection with Pseudodactylogyrus anguillae (Yin et Sproston) in August was 52.4%, and in October 17.2%, while the mean intensity of infection in the same periods was 4.0 and 1.2 individuals, respectively. The prevalence of infection with Anguillicola crassus Kuwahara, Niimi et Itagaki was 4.8 (August) and 20.7% (October), while the mean intensity was 1.0 and 2.5 individuals. Releasing parasite-infected stocking material is harmful from the perspective of fisheries management and simultaneously increases the area of occurrence of the parasites.