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

species commonly occurs in many regions from Europe to Australia. The development of the parasite has been studied thoroughly by Jarecka ( 1970), Kozicka ( 1971 ), Scholz ( 1989) and Priemer and Scholz (1989). Relatively few data are available on the intrapiscine stages of the parasite. Of tapeworms belonging to the order Cyclophyllidea occurring in Europe, four species of Dilepididae, i.e. P. scolecina (Rudolphi, 1819), Gryporhynchus pusillus Nordman, 1832, Valipora campylancristrota (Wedl, 1855) and Neogryporhynchus cheilancristrotus (Wedl, 1855) can be found in fishes (Dubinina, 1987). Many data have been published in the literature on the cyst wall structure of Cyclophyllidea larvae (Cysticercus, cysticercoid, coenurus, echinococcus) (Voge 1961, Slais 1973, Slais et al. 1971, Neradová-Valkounová 1971), while the analogous structures of plerocercus larvae of the family Dilepididae have not been studied yet. This paper reports on those studies of the Hungarian cestode fauna which demonstrated the adult and larval stages of P. scolecina from aquatic birds and fishes. The results obtained on the intrapiscine location and cyst wall structure of the plerocercus are also presented. MATERIALS AND METHODS The data on the adult stages of P. scolecina were obtained during the parasitological dissection of cormorants submitted to the Zoological Department of the Hungarian Natural History Museum. The detection and histological processing of plerocercus larvae were done during the work aimed at surveying the parasitic infections of the fish population of Lake Balaton. In the period between 1986 and 1990, a total of 45 cormorants originating from the region of Lake Balaton (Kis-Balaton, Keszthely Bay) were subjected to complete helminthological dissection. The cestodes collected from the gut were fixed in 4% hot formalin solution and stained with hydrochloric carmine. Identification was based on the examination of the inner organs as well as the shape and size of the rostellar hooks. Fish specimens were examined during a survey of the parasite fauna of Lake Balaton fishes. In the course of that work, in 1994 a total of 299 specimens belonging to 15 fish species were subjected to full parasitological dissection (see also Molnár and Székely, 1995). These fish included 60 specimens of bream (Abramis brama) and 19 specimens of gibel carp (Carassius auratus gibelio). In the subsequent two years (1995 and 1996) 48 and 53 breams were dissected, respectively. During the three years of the survey, a total of 164 specimens of 6 other cyprinid species (Cyprinus carpio, Blicca bjoerkna, Rutilus rutilus, Scardinius erythrophthalmus, Pelecus cultratus and Alburnus alburnus) were examined. Whenever this was possible, the fish were transported to the laboratory alive at two-week intervals, and were then kept in flow-through type aquaria until killed. Dissection was carried out under a stereomicroscope: either the occurrence of helminths was recorded only or the helminths were fixed for further examinations. Some of the Paradilepis plerocerci found in the samples were studied under a coverslip alive or after having been cleared in lactophenol; the majority, however, were stored in 70% alcohol. The plerocerci were identified on the basis of the size and shape of their rostellar hooks. For histology, pieces of the infected gut and bile duct portions were fixed in Bouin's solution for 4 hours, washed in 80% alcohol, embedded in paraffin, and cut into 4 pm thick sections. The sections were stained with haematoxylin and eosin. The photographs were taken with the help of a Jenaval photomicroscope.