Sealworm Pseudoterranova decipiens s.s. infection of European smelt Osmerus eperlanus in German coastal waters: ecological implications.

European smelt Osmerus eperlanus (n = 501) from the German Wadden Sea (North Sea) near the city of Cuxhaven were examined for their infestation with parasitic anisakid nematodes, especially with sealworms of the genus Pseudoterranova. The distribution of third-stage larvae (L3) in the musculature and viscera of the fish was analyzed. In total, we isolated 543 L3 from the hosts' body cavity and musculature. A subsample of 105 larvae were identified as the (sibling) species P. decipiens s.s. using direct sequencing of the highly variable ribosomal ITS1-5.8S-ITS2 genetic marker. The mean abundance was 1.1, the mean intensity was 2.3 P. decipiens s.s. and the prevalence was 47.3%. Total length and total weight, but not Fulton's condition factor (K), were significantly different in infected compared to uninfected smelt. No correlation was found between the total length of infected fish and the intensity of anisakid nematodes. The vast majority of P. decipiens s.s. was found in the musculature of the smelt. More than half (55.7%) of all nematodes were located in the 3 parts of the epaxial musculature, whereas 18.4 and 26.0% were found in the hypaxial musculature and the compartments of the tail muscles, respectively.