The occurrence of parasites in bream (Abramis brama L.), roach (Rutilus rutilus L.) and pike perch (Stizostedion lucioperca L.) in the Wloclawek Dam Reservoir on the river Vistula

Fish caught in the Włocławek Dam Reservoir during the years 1982-83 in April, July and August were parasitologically, anatomopathologically and histopathologically examined (cf. tab. 1). For histopathological examination fresh and stained permanent slides whenever necessary were made. In the studied fish parasitic protozoans (Flagellata, Sporozoa and Ciliata) as well as metazoans (flukes, tapeworms, nematods, crustaceans and, sporadically, molluscan glochidia) were found to occur. Within the first group the most important with respect to the extensity, and in some months also the intensity of infection were the Sporozoa of the genus Pleistophora (Microspora), then Myxobolus mülleri (Cnidosporidia) and Rhabdospora thelohani, within the second group - metacercariae of Diplostomum spathaceum and Tylodelphys clavatum. The parasite fauna of the bream and roach does not show any significant qualitative or quantitative differences, while in the parasite fauna of the pike perch - beside the parasites typical of this species - the parasites found also in the bream and roach i.e. in the cyprinids, dominate both qualitatively and quantitatively. Beside specific changes, characteristic of the infection with the parasitic metazoans, a higher intensity of invasion, especially in the case of Sporozoa, is accompanied by pathomorphological changes such as tissue damage, necrosis, blood supply disturbance swelling, inflammatoiry reaction with cell infiltrations and general emaciation. Such changes were not found in the great part of the fish stock, with a low intensity of infection