The Roles Of Salinity And Microalgae On Infectivity Of White Spot Syndrome Virus (WSSV) In Penaeid Shrimp

From its discovery in the north part aquacultural district of Asia in 1990s,white spot syndrome virus (WSSV) has spreaded to north America and other parts of the world. Its host is abroad and its virulent is strong, which make it become the main restrictive factor in world aquaculture. White spot syndrome is still not resolved completely because of the latent infection and kinds of spreading methods of WSSV. But there is a developing awareness that WSS is an end result of a complex interaction of shrimp, its environment and the pathogen. So the elementary preventive method, which is aimed at nosogenetic factors and dangerous factors leading to WSS, is an effective way.Lots of studies have been done on the effects of environmental factors on growth and survival of cultured shrimps. However, little work is done on the effects of environmental factors on marine crustaceans with infectious diseases. Salinity is one of the most important parameters of the culture environment for marine shrimps. In this article, we firstly established latent infection method through such indexes as nested-PCR, dot blot hybridization and cumulative mortality rates, then the effect of salinity on outbreak of WSS in infected Fenneropenaeus chinensis was studied. The role of microalgae (for example:Chlorella )played in WSS breaking out was also studied in our experiment. Results indicate that the hemocyte phenoloxidase(PO) of groups dropped 8 salinities in 1h declined sharply in relation to the control groups; Group that its salinity has been changed acutely is detected to carry more copies of WSSV than that of its correspondinggroup with time goes on. After 72h of salinity changed, the group dropped 8 salinities in 1h carried about 3 times of WSSV than that of control group. The more scale the salinity drops, the more scale the indexes of shrimps(or WSSV) changed. So salinity is one of the crucial inducements to the outbreak of white spot syndrome, its variation can lead to the outbreak of WSS from latent infection. Chlorella carried certain number of WSSV which could only be detected by nested-PCR. Adult shrimp could not be infected by the WSSV carried by Chlorella in our experiment but the detection result of little shrimp is positive. What on earth the role of microalgae plays in WSS breaking out? There is still a lot of work need to do.