PARASITOSES IN THE FRY OF SELECTED FRESHWATER FISH SPECIES UNDER THE CONDmONS OF STRIPPING AND REARING

Navratil S.: Parasitoses in the Fry of Selected Freshwater Fish Species under the Conditions of Stripping and Rearing. Acta vet. Bmo. 60. 1991: 357-366. During the period from 1984 to 1989. the problem of parasitic invasion into the artificially reproduced and reared fry of the freshwater fish species (Barbus barbus, Chondrostoma nasus. Leuciscus cephalus, Aspius aspius) wereinvestigated at a specialized fish breeding farm ofthe Czech Angler's Union in Tfeb1C!-PouSov situated on the river Jihlava (the Danube river basin). The invasion with parasites was investigated in 979 fish specimens (846 juvenile. 133 adult) of the selected species and in 257 fish of other species. The reared fry of the selected fish species were found to be' endangered already in their first days ofHfe. predominantly by ectoparasitic protozoa with not definitely formed host specificity. Thus optimal rearing conditions have to be assured. along with regular examination of the health status. Efficient preventive antiparasitic baths have to be applied. It is advantagenous to complement these measures with an effective way of sanitation of the fish-rearing farms. by the investigation of the health status of fish in the feeder of the fish-hatchery and rearing pond with its regulated stocking, . or possibly by declaring relevant areas as being protected with the introduction of a closed turnover of the parent fish shoal. Barbus barbus. Chondrostoma nasus. Leuciscus cephalus. Aspius aspius. ectoparasitic protozoa. zoooeterinary measures . The industrial development. intensification in agriculture and the growth of residential areas are the principal sources of water pollution. The living conditions in water courses have changed in recent years due to waste water discharge, run-offs from surface drainage, the increase of eutrophisation, acid rain, and water course regulation. This caused that some of the fish species have lost their viability in these waters, and in other the fish-planting cannot be ensured by a natural reproduction. It has thus been necessary to proceed to artificial stripping. rearing and planting of these fish species. This concerns also the investigated fish species (barbel Barbus barbus. nase Chondrostoma nasus, chub Leuciscus cephalus and asp Aspius aspius). The introduction of the above mentioned modem technologies of reproduction and rearing results in new problems concerning the health status of fish. Technological processes of stripping and rearing of fry for the fish species mentioned above have been worked out only recently but in some cases they are still missing. During our investigation only the methods of stripping and rearing for the barbel species were available in a complete form applicable for our fishery (Krupka 1987). Pecha (1986) reported on his experience with stripping and rearing of the asp. The method of artificial stripping and rearing of the investigated species is thus based on the procedures worked out for other fish species and on the experience of hatcherymen and breeders. The success of stripping and rearing, with the smallest possible health problems and losses