*Corresponding author: Dr. M. Pietrock, phone: x30-641 90 565, fax: x30-641 81 750,
From May 1993 to April 1995 a comparative study on the seasonal dynamics of Phyllodistomum folium (von Olfers, 1816) infection was carried out on 633 blue bream, Abramis ballerus (L.) and 266 ruffe, Gymnocephalus cernuus (L.) from the Oder River (Germany/Poland). In blue bream, the monthly prevalences and mean intensities of infection varied irregularly throughout the year: prevalence values attained up to 50% and mean intensities reached 7.6 (range: 1-34) trematodes per infected fish. Conversely, in ruffe a temperature dependent occurrence of P. folium was observed: both the prevalence and mean intensity of infection were significantly higher at a water temperature beneath 10°C than above, with a highest monthly prevalence of 60.8% and a mean intensity of 2.9 (range: 1-7) P. folium. Juvenile and gravid trematodes were found in blue bream and ruffe at all seasons. Based on this study, it is concluded that (a) infection of fish is possible throughout the year, and that (b) modifications in course of infection are determined by the host species rather than on water temperature.