Comparative study on immune response of Fenneropenaeus indicus to Vibrio alginolyticus and white spot syndrome virus

The present study was carried out to examine the histopathological and immunological changes in Vibrio alginolyticus-injected or white spot syndrome virus (WSSV)-injected shrimp Fenneropenaeus indicus. The results obtained were compared with healthy shrimp. After the injection of WSSV or V. alginolyticus in the shrimp F. indicus showed mild to extensive hemocytic infiltration in the muscle and were often accompanied by melanization. Hemocytes were infiltrated at the site of injection with V. alginolyticus showed higher than the WSSV-injected site. In the present study, WSSV- and V. alginolyticus-injected shrimp showed proPO, O2− and clotting time were significantly higher than those of the control groups, whereas THC and superoxide dismutase were significantly lower than control groups. The increase of PO after stimulation seems to be attributed to the activation of proPO by V. alginolyticus that contains bacterial lipopolysaccharide during the course of non-self-recognition, while the activating mechanism of WSSV is still unknown. Superoxide anion levels and superoxide dismutase levels showed that the activity of NADPH oxidase responsible for the release of superoxide anion increased together with a decrease in the activity of superoxide dismutase responsible for scavenging superoxide anion. Subsequent studies and comparison of results showed that prolongation of clotting as a result of hemocytes disappearance and the high levels of protein in the hemolymph of WSSV-infected shrimp due to the protein of WSSV.