Dr. Murai Éva szerk.: Parasitologia Hungarica 14. (Budapest, 1982)
MATERIALS AND METHODS Our investigations were carried out between April 1979 and October 1981. One- to three-summer old common carp from different fish ponds of Hungary were submitted regularly to the laboratory either for routine veterinary examination or for research purposes. Field inspections were also conducted at two week intervals, and included about 20 fish per farm. In the period indicated above 6 155 carp were examined during routine diagnostic work and 1 300 carps were dissected in our laboratories where parasitological, bacteriological and histopathological examinations were made, mainly on young fry. Parasitological examinations of fish that were killed or that had died recently were made under a dissecting microscope. Impression smears and squash preparations of the gills, kidneys, liver, spleen and swimbladder were also taken. The gills and the aforementioned organs of two fish per sample were fixed in 109? formalin and cut by cryostat for routine purpose. Organs showing alterations were fixed in aqueous Bouin's fixative embedded in paraffin wax and cut into 4 to 8 urn sections which were stained with haemotoxylin and eosin. Before fixation the lumen of the swim bladders was filled up with egg-white. Spores obtained from myxosporean cysts were examined either in fresh or after embedding in glycerine-jelly. Measurements of spores were taken on the material in glycerine-jelly. RESULTS The Thelohanellus infection described by JENEY (1979) was regularly observed in common carp fry populations during the summer breeding period. In 1979 the infection was demonstrated only at the eastern border of the country, in fish farms along the water-system of the River Körös. By 1981, however, Thelohanellus infection appeared in some fish farms of Western Hungary and in the eastern part of the country infection became general. In some fry-rearing ponds of Eastern Hungary the prevalence of infection reached 60 to 90%, and the intensity, 20-40 cysts per fish. In 1981 cysts were detected on the fins of even two- and three-summer old carps. Infection was restricted to the fins, and the thick-walled cysts of 1-2 mm in diameter were localized close to the fin rays (Fig. 1). The developing cysts deformed the structure of the rays, and produced cartilageous outgrowths from them. Cysts were surrounded by a thick capsule consisting of loose connective tissue which was covered by intact epithelium toward the surface of the fin (Fig. 2-3). The first signs of infection could usually be detected by early July, and the infection dropped off at the end of August but at latest in October when the cysts burst. Although in heavy infection the breakdown of fins was observed, losses exclusively due to thelohanellosis were not recorded. Thelohanellus stages developing in organs other than fins were found only in 1981 when during the histological examination of two-summer old carp originating from a pond farm established on the watersystem of the River Tisza, relatively thin-walled cysts (Fig. 4) containing Thelohanellus-like spores were found in the swim bladder serose. More thorough examinations revealed that about 20% of the fish harboured lens-shaped cysts with a diameter of 1-3mm which were located on the swim bladder serosa Legends to Figures Fig. 1: Common carp fry infected with Thelohanellus nikolskii cysts on the fins. Original size. Fig. 2: Histological section of a semimatured T. nikolskii cyst. H. E. x 100. Fig. 3: Histological section of a young T. nikolskii cyst. H.E. x 100. Fig. 4: Histological section through the swimbladder wall. T. hovorkai cysts containing some spores. H.E. x 100. Fig. 5: T. nikolskii spores, x 1100. Fig. 6: T. hovorkai spores, x 1100.
