Dr. Murai Éva - Gubányi András szerk.: Parasitologia Hungarica 28. (Budapest, 1995)

The parasite fauna of the Volga pike-perch (Table 2) is practically identical with that of the pike-perch. It was interesting to note that in this fish species the individuals of E. sieboldi could only be found, in lower numbers, on the operculum. Achtheres percarum, which commonly occurred on the pike-perch, could not be demonstrated on the Volga pike-perch. As regards the protozoan fauna, the Goussia species causing nodular coccidiosis and revealed by an early spring examination should be mentioned. Only aimed studies concentrating on a few species were carried out on the parasite fauna of the eel (Table 3). First of all the infection and swimbladder lesions caused by Anguillicola crassus were monitored; however, we consistently looked for the occurrence of two fin parasites, Myxobolus portucalensis and Daniconema anguillae as well. The commonest parasites of the bream (Table 4) included Myxobolus species and E. sieboldi specimens on the gills, the imago stages of Asymphylodora immitans in the gut and the metacercaria stages of Apophallus muehlingi in the fins. In the May to mid-June period female specimens of Tracheliastes maculatus were found on the skin of all breams examined. The species indicated in the table as Myxobolus sp. I, II and III seem to represent separate species differing in location and morphology. In all probability, one of them found on the scales is a hitherto undescribed new parasite. In all but two cases, the developing female specimens of Ph. ovata were detected from breams infected with Ligula intestinalis plerocercoids. At the same time, the so-called "retarded", non-developing specimens of Ph. ovata were found in the swimbladder of all breams examined. The data shown in the tables indicate lower-than-actual prevalence values, as not all fish were dissected in physiological saline, which procedure is a precondition of reliable detection. Only large sized, several years old specimens of gibel carp could be obtained from the fishermen. These fish were found to have a surprisingly low degree of parasitic infection (Table 5). At the same time, two protozoans (Hoferellus carassii and Goussia carpelli) proved to be very common parasites. As a fish species that has recently migrated into Lake Balaton, the river goby is infected by few parasite species (Table 6). No specific parasite was detected among the species found. At the same time, the river goby showed a conspicuously intensive infection with 3rd stage larvae of the eel parasite A. crassus. As regards the parasitic infections of other fish species (Table 7), the low-intensity infection of the common carp and the extremely rare occurrence of parasite-free individuals should be mentioned. The intensity of infection of other cyprinid species corresponds to that observed in the bream. In the sheatfish fry and the ruffe (Table 6), infection with 3rd stage larvae of A. crassus was a conspicuous finding. In the sheatfish this infection even caused mortality due to ascites. DISCUSSION Studies on the parasite fauna and seasonal occurrence of fish species living in a given habitat require extremely lengthy and consistent work. Studies of such type have first of all been carried out by specialists from the former Soviet Union. Of them, Shulman and Chernisheva (1969) studied the parasite fauna of fish in Lake Selinger, Allamuratov (1974) in the watershed area of the Surchandarya, while Pugachev ( 1984) studied it in fish derived from some rivers of North-east Asia. Data on the parasite fauna of fish in different reaches