| Cryptocaryoniasis is a fatal parasitic disease caused by Cryptocaryon irritans parasitizing marine teleost surface. In recent years,cryptocaryoniasis has become one of the important diseases in large yellow croaker(Pseudosciaena crocea), which has seriously harmed the healthy development of large yellow croaker aquaculture, but so far has not an effective method of prevention. In order to provide theoretical basis and practical guidance for the control of C. irritans, we carried out systematic researches on the formalin, removal of tomonts of C. irritans and Immune prevention to control of the parasite.1, Study on prevention and treatment of C. irritans infection for Large yellow croaker by formalin, the present study has evaluated the in vitro and in vivo anti-parasitic efficacy of formalin against the ciliate C. irritans. Toxicity of formalin against the juveniles of large yellow croaker was also tested. The obtained results showed that the lowest concentration of formalin to kill theronts within 10, 30, 60 and 120 min were 62.5?62.5?31.3?5.6 mg/L and to kill tomonts within 1, 2, 4 h were 150, 75, 75 mg/L, respectively. The large yellow croaker24-, 48-, 72-, 96h-LC50 exposed for formalin were 394.7 ? 365.3 ?334.4 ? 322.8 mg/L,respectively, the safe concentration was 119.57 mg/L. It can effectively control Cryptocaryon irritans infection of large yellow croaker treating with 125 mg/L formalin for2 h, the survival rate was significantly higher than 75 mg / L and control groups. The results showed that the prevention and treatment of C. irritans infection for large yellow croake may have within the safe concentration of formalin.2, The interruption of transmission route is an important strategy for the prevention and treatment of parasitic diseases. To control this disease, we established a method to interrupt the life cycle of C. irritans via the removal of tomonts of C. irritans by exchange of a tank liner or by rotation of fish between tanks. After treatment, a daily food consumption(DFC),relative infection intensity(RII) and survival rate of each group were observed. At 4-weeks post infection, serum immobilization titers of tank liner removal group(Group I), rotational culturing group(Group II) and uninfected control group(Control) were detected and challenged them with C. irritans theronts at a lethal dose. Results demonstrate that Group I or Group II can effectively control C. irritans infection, DFC, RII and survival of fish was similar to that of the Control. In addition, the serum titers of the Group I and II were significantly higher compared with Control. The survival rates of Group I, Group II and Control were 88.3%, 93.3%, 66.7%. Treatment of of Cryptocaryon irritans infection for large yellow croaker via the removal of tomonts of C. irritans by exchange of a tank liner.The obtained results showed that the survival rate of exchange the tank liner groups every 2or 3 days were significantly higher than every 4 days groups and control groups. In conclusion, the method can provides an ideal means for controlling C. irritans in small scale culture systems and it is better than chemical methods.3, In this experiment, C. irritans theronts were respectively combined with white oil and Quil-A adjuvant to form oil adjuvant inactivated vaccine and C. irritans immunostimulating complexes(ISCOMs). White oil group and ISCOMs group were set,with PBS as control group. Immunity was used intraperitoneal injection(20?l, 10,000 theronts per fish) and reinforced in week 2. Specific antibody titres of fish serum were determined at week 0, 1, 2, 4, 6 and 8. At 4-weeks and 8-weeks post immunization, the fish were challenged with a lethal dose of theronts and the death rate was collected. At 8-weeks post immunization, the fish were infected with a sub-lethal dose of theronts, gills were taken to count the number of trophozoite in each group and the relative infection intensity was calculated at 48 h. At 72 h, tomonts were collected and their diameters were measured.Results demonstrate that specific antibody of white oil group and ISCOMs group can be detected in some immunised fish at week 1 and the peak was at week 6, respectively with antibody titer of 1:359.2 and 1:430.7. At week 4 and 8, the fish after challenge by a lethal dose of theronts, and the death rates of white oil group and ISCOMs group were significantly lower than that in the control group. At week 8, 15 fish at each parallel group were challenged by a sub-lethal dose of theronts, the reduction rate of relative infectionintensity in white oil group and ISCOMs group were 37.2% and 30.7% and the size of tomonts were 40.2% and 13.4% less than that in control group, respectively. These findings indicated that C. irritans inactivated vaccine had a strong immunogenicity to large yellow croaker and it provided good protection against challenge with C. irritans and effectively reduce the infection of C. irritans. |
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