Dr. Murai Éva szerk.: Parasitologia Hungarica 25. (Budapest, 1992)

Parasit, hung., 25: 79-83,1992 © Hungarian Society of Parasitologists Losses caused by the snail commensalist Chaetogaster limnaei Baer, 1827 among sterlet larvae (Acipenser ruthenus L.) Ferenc BASKA

1 and Flóra BÓNA-PUPPÁN

2 Veterinary Medical Research Institute, Hungarian Academy of Sciences, H-1581 Budapest, P. O. Box 18, Hungary TEHAG, Százhalombatta, Hungary (Received 30 October, 1992) Abstract: In 1991, substantial mortality was observed among sterlet fry cultured in the hatchery of TEHAG. The mortality was caused by the oligochaete Chaetogaster limnaei known as a commensalist of snails. Physa acuta, a snail infected by this worm was found in a great number in water-conduits. The commensalist sparely-bristled worms actively moving in the gill and oral cavities and on the body surface prevented the first breath-taking and food intake of immature larvae. As a result, occasionally the entire culture died out. Medication attempts with different doses of formaldehyde, trichlorphon and mebendazole were also made to control the problem. Keywords: Sterlet larvae, Oligochaeta, Chaetogaster limnaei, pathogenic commensalist, treatment INTRODUCTION Studies on the parasite fauna of acipenserids have a history of at least two hundred years. Helminths have been demonstrated from these fishes since the end of the 18th century. Investigations into the protozoan fauna of acipenserids and the description of new species were made possible by technical progress at the beginning of the 20th century. Despite the fact that the work has been lasting for a long time, new species descriptions are still being published. These works report on coccidian and myxosporean infections of the sterlet, a topic little studied so far (Molnár 1986, Baska 1990). The largest body of data on parasitoses of acipenserids living in the waters of Eurasia was supplied by Russian and Soviet researchers. Bychowsky (1962) fully reviewed the parasite fauna of the 10 acipenserid species native in the Soviet Union, including the