576 flounders were collected from the Pomeranian Bay, Gulf of Gdańsk and the open sea off Łeba in the period from March 1997 to February 1999. 105 flounders were collected in October 1999 from Lake Łebsko. 143 out of 681 fish were...
more576 flounders were collected from the Pomeranian Bay, Gulf of Gdańsk and the open sea off Łeba in the period from March 1997 to February 1999. 105 flounders were collected in October 1999 from Lake Łebsko. 143 out of 681 fish were infected. 1557 acanthocephalans of Pom-phorhynchus laevis were recovered. The mean intensity of infection and prevalence were calculated. One can conclu-de that the intermediate host Gammaridae plays a signifi-cant role in the occurrence of P. laevis, and thus in the pre-valence and intensity of infection. The age of the fish and the occurrence of P. leavis were correlated. Young fish, no older than one year, were infected by P. leavis. Three- and four-year-old fish were the most susceptible to infection. Older fish, aged five years or more, were less susceptible. Only one encapsulated acanthella was found on the go-nads; there was therefore a possibility that Platichthys flesus could act as a paratenic host. In the Skagerrak or in the north-western Baltic Sea P. laevis commonly occurs in the form of encapsulated larvae. This life cycle strategy is probably due to the presence or absence of predators of P. flesus and the final host of P. laevis.
