Anguillicola crassus Kuwahara, Niimi et Itagaki, 1974 is an Asian parasitic nematode that was introduced to Europe and inhabits the swim bladder of eels. In the 2002-2005 period, 237 eels, Anguilla anguilla (Linnaeus, 1758), from Lake Wdzydze were examined for the occurrence of the nematode. 79.3% of the fish were infected, at a mean intensity of 7.2 nematodes per fish. Morphological measurements of the observed A. crassus are presented. This is the first published report of A. crassus in eels from Lake Wdzydze.
