The Studies On Pathogeny, Pathology, Medication And Immunoprophylaxis Of Ichthyophthiriasis Of Freshwater Fishes

Ichthyophthirius multifiliis is a globly distributed parasite which obligately parasites on freshwater fishes, and caused ichthyophthiriasis. The disease causes high mortality under the conditions of intensive aquaculture, and a great sum of money loses to the disease annually.With the temperature rising from 4℃ to 32℃, the thickness of the cysts became thinner, and so the time needed to form cysts got shorter; the period from a cyst develop into disinfectious theronts was shorten with the temperature rising from 8℃ to 26℃; the energy index of infectious theronts during the temperature range (23-26℃) is the highest; /. multifiliis parasites on different fish species varied in amount, body size and their preference to parasitic sites.In order to determine whether differences exist between histopathology of scale fish and that of no scale fish infected by /. multifiliis, we choose Coreius guichenoti, a species of scale fish, and Leiocassis longirostris Gunther, a species of no-scale fish, to observe the histopathology. The results showed that /. multifiliis mainly infected the skin, gills, fins and cirruses of the juvenile Leiocassis longirostris Gunther and Coreius guichenoti] its theronts were occasionally found in the tissues next to the muscles of Leiocassis longirostris Gunther. The parasite caused hyperplasia of the host epidermis and connective tissues, and were subsequently surrounded by the hyperplastic tissues. Some infected sites on skin and cirrus of the juvenile Leiocassis longirostris Gunther were usually congested and ulcerated, and the pigment layer partly disappeared. Some infected sites on skin and gill of Coreius guichenoti were also ulcerated, and the epithelium partly disappeared; the gill were the most seriously damaged organ; the gill filament shape were extruded by hyperplastic tissues caused by parasites, and stuck together, and even its main shape could hardly be distinguished. Both the infected fins of the two fish species were extruded by the trophonts of the parasite, and the seriously infected fins and cirruses were disappeard. Based on the histological study of the two fish species infected by the parasiticciliate.The high mortality rate of the infected larvae and the possible treatment measures were discussed.Different drugs and a series of concentrations of some drugs were used to test whether they could kill /. multifiliis in free-living stage. The results of the experiments showed that formalin at 200-300ppm, salt at 2%, H2O2 at 200ppm, the mixture of capsicum and ginger, the fruit of Melia azedarach were 100% effective in killing free-living parasites. Salt at 1%, ginger, Melia azedarach, Vitex negundo, the mixture of copper sulfate and iron sulfate at 0.7ppm were ineffective against any stage of the parasite.In light of advantages of immunoprophylaxis for treatment of the Ichthyophthiriasis, an effort was made to determine whether fish exposed to killed parasite preparations can resist subsequent lethal challenge of infectious theronts. Both the route of administrations and the effects of specific antigens in the parasite stages were studied. All Goldfish died after vaccination with live trophonts by pericardium-antrum injection and with formalin-fixed trophonts or theronts by orally pouring before challenge. Although all the test groups almost showed 100% mortality following a challenge, there was a consistent difference in days to death between control and test group animals. Goldfish vaccinated both with formalin-fixed trophonts, formalin-fixed theronts, cilia membrane protein of trophonts by pericardium-antrum injection and with live trophonts by pouring orally, had a much greater degree of protection when all control fish died. Every ten days after vaccination, immobilization antibody titer of serum and immobilization antibody titer of mucous of both test groups and control groups were tested. The results showed that all vaccines except the live theronts and freeze-thawed lysates of theronts could elicit goldfish to produce the immobilization sera an...