Study On Prophylactic Vaccination Against The Vibriosis Of Large Yellow Croaker (Pseudosciaena Crocea Richardson)

The serotype of 66 strains of Vibrio harveyi isolated from large yellow croaker(Pseudodciaena crocea Richardson) infected by vibriosis was tested in this study. The juvenile large yellow croakers, which cultured in the cage in Xiangshan Bay , were vaccinated with formalin killed V.harveyi (F-VH) of the virulent strains by immerse route , The results were summarized as follow. 1. The serotype of V.harveyiAntiserum against 12 formalin killed V.harveyi strains were prepared in rabbits. The serological type were studied by cross-agglutinating test and gel diffusion reaction. The results showed that 54 of 66 strains V.harveyi isolated from Ningbo can be classified into four serological types(LY1, LY2, LY3, LY4), the serotype of the other 12 can not be determinated by cross-agglutinating test and gel diffusion reaction. And the tests denonstrated that these strains had mass heat-liable antigen, which is sensitive to heat. 2.Efficacy of immersion with V. harveyi vaccineLarge yellow croakers were immersed with F-VH vaccine with the concentration of 108cells/mL, 107cells/mL, 106cells/mL, and the treating time 1min, 10min and 60min, respectively. After vaccinating, the fish was cultured in net cages. Relatively survival percent (RSP) was tested 8 to 18 weeks postvaccination. The results showed that RSP was the highest during 8~11 weeks postimmersion, reached 95%~100%, and then slowly declined to 70%~80% during 16-18 weeks. Field statistics released the trend, comparing to the control group, the vaccinated groups infected with less diseases, diseases broke later, and the diseased fish recovered sooner. The survival percent of the immunized groups reached 80%~95%, which was significantly higher than the control groups. The fish at different day-age, 40 d, 75 d and 100 d post hatch, were immunized and RSP was tested afterwards. The results indicated that 40 d juvenile also acquired protective immunity by immersing. Boost vaccination was carried out 54 d after the first immersion. High RSP level was detected during 8-16 weeks post boosting, which was much higher than thenon-boosted group. It is possible to improve the resistant to V.harveyi infection and survival rate of juvenile large yellow croaker through immerse vaccination with F-VH vaccine.