The effect of different salinities on mortality and histopathological changes of SPF imported Litopenaeus vannamei, experimentally exposed to White Spot Virus and a new differential hemocyte staining method

  Shrimp farmers have been suffering from loss of production due to White Spot Disease (WSD) in the last decades. A few studies focused on the environmental factors predisposed WSD. Our study aimed to investigate the effects of the different salinities on occurrence of WSD. The treatments were ۳۰ ppt, ۴۰ ppt and ۵۰ ppt in triplicate and corresponding untreated control groups. White Spot Virus (WSV) was intramuscularly injected to the shrimp in whole treatments. PCR and histopathological findings within the measurement of some hemolymph parameters such as Differentiated Hemocyte Count (DHC), Total Hemocyte Count (THC) and Total Plasma Protein (TPP) were carried out. A positive result was observed for the occurrence of the antigen of the WSV obtained from the samples of each treatment of salinity due to the challenging treatments with the WSV. Mortality at the salinity of ۳۰ ppt began at ۷۲ h post inoculation as well as the salinity of ۴۰ ppt, but at ۵۰ ppt it started after ۵۰ h. The Minimum and maximum count of mortality at the salinity of ۳۰, ۴۰ and ۵۰ ppt were ۳.۵, ۸.۵ ۰.۵, ۴.۵ and ۱.۵, ۷.۵, respectively. No mortality was observed in the untreated control groups of ۳۰, ۴۰ and ۵۰ ppt during the experiment. It is concluded that the higher and the lower salinity, lesser or greater than the normal condition in exposed to WSV could lead to severe mortality of WSD.