The occurrence of Pomphorhynchus laevis (Muller, 1776) (Acanthocephala) and the age of the flounder (Platichthys flesus, L.)

576 flounders were collected from the Pomeranian Bay, Gulf of Gdansk and th e open sea off Leba in the period from March 1997 to February 1999. 105 flo unders were collected in October 1999 from Lake Lebsko. 143 out of 681 fish were infected. 1557 acanthocephalans of Pomphorhynchus laevis were recover ed. The mean intensity of infection and prevalence were calculated. One can conclude that the intermediate host Gammaridae plays a significant role in the occurrence of P. laevis, and thus in the prevalence and intensity of i nfection. The age of the fish and the occurrence of P. leavis were correlat ed. 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 acant hella was found on the gonads; there was therefore a possibility that Plati chthys flesus could act as a paratenic host. In the Skagerrak or in the nor th-western Baltic Sea P. laevis commonly occurs in the form of encapsulated larvae. This life cycle strategy is probably due to the presence or absenc e of predators of P. flesus and the final host of P. laevis.