Dr. Murai Éva - Gubányi András szerk.: Parasitologia Hungarica 29-30. (Budapest, 1997)

roach (Rutilus rutilus) population of Kis-Balaton 4 protozoan and 6 metazoan species were detected. Six protozoan and 3 metazoan parasite species were recorded from the bleak (Alburnus alburnus), 2 protozoan and 2 metazoan species from the white bream (Blicca bjoerkna), and only 3 metazoan species from the tench (Tinea tinea). With the exception of a single specimen, the pikeperch (Stizostedion lucioperca) specimens included in the sample represented the first-summer age group. Of the two protozoan parasites found in pikeperch, the gill-parasitic Trichodina sp. not identified to the species level may be much more common than it appears from the data, as these ectoparasites disappeared from the fish already after a short time spent in aquarium. Five metazoan parasite species were detected in Kis-Balaton pikeperch: the most prevalent of these were Thylodelphys clavata and Diplostomum spathaceum detected from the eye. In the perch (Percafluviatilis) we found 1 protozoan and 2 metazoan parasites, while in the single specimen of ruffe (Gymnocephalus cernuus) that we examined 3 metazoan parasites were found. The parasitological dissection of pikes (Esox lucius) revealed the presence of 5 protozoan and 3 metazoan parasite species which caused an infection of low prevalence and intensity in the fish examined. One out of the three European catfish (Silurus glanis) specimens examined was negative for parasites while the other two were found to have only a single parasite species, Diplostomum spathaceum. DISCUSSION As a previously drained wetland which has recently been reconstructed, in the biological sense Kis-Balaton rates as a rather variable habitat having an unsettled limnofauna and, therefore, experiencing continuous changes in the structure, feeding conditions and health status of its animal species including fish. These changes often manifest themselves in the massive growth and subsequent reduction of the population of a given fish species. Therefore, systematic animal health monitoring of the area is essential. Survey of the parasite fauna constitutes an important component ofthat monitoring. Earlier, studies of this type were conducted by Soviet authors (Akhmerov and Bogdanova 1957, Kamenski and Ponomareva 1964, Bogdanova and Nikolskaya 1965, Iskov and Koval 1965, Komarova 1972, Iskov 1975, Iziumova et al. 1982) who surveyed the parasite fauna of fish in different reaches of rivers before the establishment of water reservoirs and then continuously monitored changes of the parasite fauna in those reservoirs. Similar surveys have also been performed by Hanek and Molnár ( 1974) on fishes of a new water reservoir naturally created on the Matamek River by a landslide. Our present survey also deals with such a situation, as in the case of Kis-Balaton one part of the water reservoir has already been populated with fish while the other part is currently being filled. A sound parasitological survey would require the processing of large numbers of fish species and specimens, and should include all species of fish parasites. In the course of this study, however, the processing of a sufficiently large sample size was not possible; nor was there an opportunity for the in-depth study of some parasite species difficult to identify. Therefore, many parasites have been identified to the genus level only. This especially applies to the mostly specific representatives of myxosporeans and monogeneans. It is obvious that besides Dactylogyrus auriculatus, the species found to be the most prevalent in the samples, at least four other