Zió∏kowska M., Rokicki J., 2003. An attempt to determine the intermediate host forPomphorhynchus laevis (Acanthocephala) in the Baltic Sea. Acta Ichthyol. Piscat. 33 (1): 37-45. Background.A number of fish species in the Baltic Sea are known as definitive hosts for Pomphorhynchus laevis but it is unclear which of the Gammarus species is the intermediate host of this parasite. The aim of the present paper was to identify this host in brackish waters of the Baltic Sea. Material and methods. A total of 531 scuds (G. salinus, G. zaddachi, and G. duebeni)were collected from the Gulf of Gdaƒsk and the Pomeranian Bay, to determine the infection rate of those amphipods in the natural environment. Under experimental condition the scuds were exposed to infection with P. laevis in two different arrangements. In treatment one, the amphipods were kept, from May to July, in the same tank with infected flounder. In treatment two, 197 scuds were exposed to eggs of P. laevis, taken from dissected female acanthocephalans. Results. Scuds sampled from two areas of the Baltic Sea were not infected with P. laevis. Out of three Gammarus species cohabiting with infected flounder only G. zaddachi became infected. None of the scuds exposed directly to the eggs of the parasites became intermediate host of the acanthocephalan studied. Conclusion. Gammarus zaddachi is probably an intermediate host forPomphorhynchus laevis in the Baltic Sea.

Six hundred and seventy nine specimens of Platichthys flesus (L.) were caught in summer (July–September) 1998 and 1999 from three regions of the Polish zone of the Baltic Sea: the Gulf of Gdańsk, the Pomeranian Bay and the open sea off Łeba. The biometric measurements (length, weight, age) and sex of the specimens were recorded. The specimens were examined for occurrence of parasites. The intensity, relative density and prevalence of infection were calculated.