Study On Three Kinds Of Prevention And Control Measures For Cryptocaryon Irritans Infection

Crytocaryon irritans,a obligate protozoan ciliate,infects almost all marine teleosts fish in tropical and sub-tropical regions,which mainly parasitizes on the skin,gill and fin of fish.In China,cryptocaryoniasis has been refered as the second class aquatic disease.In recent years,cryptocaryoniasis has become the most serious parasitic disease in marine aquaculture in China,and cause billions of dollars in economic losses each year.Although the damage is so severe,it is difficult to prevent and control the disease for its unique parasitic site,complex life cycle,and the openness of aquaculture environment.So far,there are no very effective prevention and control measures to this disease.For this,the present study conducts experiments on the prevention and control of cryptocaryoniasis,and evaluates their effects from the following aspects:Firstly,physical control based on the “Clothing” method: The effects of temperature and host species on the time of tomonts incubation and theronts excystment were studied.The results showed that when the temperature was between 18-30°C,the residence time of trophonts on the fish body decreased with increasing temperature,especially in the range of 18-24°C,and it decreased significantly with increasing temperature.However,at 30-32°C,the residence time of trophonts did not change much.In addition,the residence time of trophonts at the same temperature is not completely affected by the species;similarly,the time of theronts excystment is also shorter as the temperature rises,especially in the range of 18-22 °C,the change is extremely significant,However,when the temperature is higher than 24°C,the change is relatively slight.The host had little effect on the time of theronts excystment,and the incubation time was almost the same under the same temperature conditions.Based on these results,the frequency and times of the cloth replacement under different temperature and host conditions were finally established and verified by in vivo experiments.Secondly,drug prevention and control: eight Chinese herbal medicine and chemical drugs were chosen to feed fish for a week,and the protection effect of each treatment was assessed by using the lethal dose of C.irritans attack.The results showed that the protection rates of diclazuril,chlorpheniramine hydrochloride(98% active ingredient),chlorophenylhydrazine hydrochloride(active ingredient 6%),artemisinin,and artemisinin + pepper mixed raw materials were extremely low.There was a relative protection rate of only 10% for chlorpheniramine hydrochloride(6% active ingredient),and the other three drugs had no protective effect.There was a 15% relative protection rate for deoxyquinacin(6% active ingredient)and deoxyquinacin(20% active ingredient),while salinomycin sodium provided a relative protection rate of 35%.Thirdly,immunity prevention and control: The protective immunity of grouper(Epinephelus drummondhayi×Blotchy rock cod)against C.irritans was determined after immunization with surface exposure or intraperitoneal injection.The results indicated that at the first month after immunization,fish in the surface exposure group showed 60% of relative percentage survival(RPS),which was significantly higher than that in intraperitoneal injection group(0% RPS);From the second months after immunization,the RPS began to increase and reached up to 60% at the third month in the i.p.injection group,but only 40% of the RPS in the surface exposure group at this time;The results of non-lethal doses of infection showed that the protective effect of surface exposure immunity was particularly prominent,and the relative infection rate could be reduced by 83%-99%.