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

(Szipola 1987, Csányi 1991, Biró 1994, Keresztessy 1995, Paulovits etal. 1995, Tölgand Biró 1995, Szabó 1996, Csányi et al. 1996, Biró et al. 1996, Tölg et al. 1996, Tátrai et al. 1996). Besides detailed studies on the fish fauna, however, the parasitic infections of fish have not been surveyed systematically. As regards the veterinary examinations of Kis-Balaton fishes, in recent years the specialists of the Central Veterinary Institute have mostly attempted to determine the causes of fish mortality after fish kills (Csaba et al. 1991, Csaba 1996). These studies usually traced back the fish kills, which were mostly limited to the gibel carp population, to oxygen deficiency or bacterial infections. To supply the long felt need for detailed fish-parasitological examinations, in 1996 our team embarked upon a parasitological survey of Kis-Balaton fishes in the framework of a 4-year project supported by the National Research Fund (OTKA) of Hungary. Fish pathology experts of the Central Veterinary Institute also participate in the project primarily by studying bacteriological problems. In the first year of the 4-year project our survey was limited to fish species of the Upper-Reservoir (the so-called Hídvégi Lake), but in subsequent years we plan to extend our studies to the parasites of fishes in the Lower-Reservoir (Fenéki Lake). Although fish-parasitological data are not available for Kis-Balaton, surveys of such type have long been conducted in Lake Balaton whose water system is connected with Kis-Balaton by the Zala River. A detailed list of earlier fish-parasitological research performed by other authors on Lake Balaton fishes can be found in the work published by Molnár and Székely (1995) on the parasite fauna of the major fish species of Lake Balaton in 1994. New studies on the parasite fauna are justified by the massive eel kill that occurred in Lake Balaton in the years 1991-1992 and then in 1995, which Molnár et al. (1991, 1994) attributed to swimbladder damage caused by the introduced nematode parasite Anguillicola crassus. Another important disease of hitherto unelucidated aetiology resulted in the pathological emaciation of breams and caused mortality in the bream population of Lake Balaton in 1994. The primary objective of our fish-parasitological studies of Kis-Balaton was to conduct a monitoring-type survey of the fish population which would enable us to call attention to the possible appearance of pathogenic parasites. Other important goals were to get to know the yet unexplored fish parasite fauna of Kis-Balaton and to look for possible fish-parasitological interactions between Lake Balaton and Kis-Balaton. MATERIALS AND METHODS The studies were carried out in the fishing season of 1996 (from 3 April to 20 November). At five sampling times, a total of 100 fish specimens belonging to 13 fish species were collected from the area surrounding the fishing establishment of the Upper-Reservoir of Kis-Balaton (Lake Hídvégi; Fig. 1) and were subjected to complete parasitological examination. The following numbers of the fish species included in our research protocol were dissected: gibel carp (Carassiw auratusgibelio) 27, bream (Abramis brama) 14, common carp (Cyprinus carpio morpha hungaricus) 12, rudd (Scardinius erythrophthalmus) 10, roach (Rutilus rutilus) 8, pike (Esox lucius) 6, pikeperch (Stizostedion lucioperca) 6, bleak (Alburnus alburnus) 4, tench (Tinea tinea) 4, perch (Perca fluviatilis) 3, European catfish (Silurus glanis) 3, white bream (Blicca bjoerkna) 2, ruffe (Gymnocephalus cernuus) 1. The parasitological findings of these dissections have been recorded. The body length of the fishes examined varied between 7 and 77 cm. Unfortunately, the species composition of fish examined at the different sampling times was not uniform as it dependent on the catch.