Effects of acute change in salinity and moulting on the infection of white leg shrimp (Penaeus vannamei) with white spot syndrome virus upon immersion challenge

In the field, moulting and salinity drop in the water due to excessive rainfall have been mentioned to be risk factors for WSSV outbreaks. Therefore, in this study, the effect of an acute change in environmental salinity and shedding of the old cuticle shell on the susceptibility of Penaeus vannamei to WSSV was evaluated by immersion challenge. For testing the effect of abrupt salinity stress, early premoult shrimp that were acclimated to 35 g L−1 were subjected to salinities of 50 g L−1, 35 g L−1, 20 g L−1, 10 g L−1 and 7 g L−1 or 5 g L−1 and simultaneously exposed to 105.5 SID50 mL−1 of WSSV for 5 h, after which the salinity was brought back to 35 g L−1. Shrimp that were transferred from 35 g L−1 to 50 g L−1, 35 g L−1 and 20 g L−1 did not become infected with WSSV. Shrimp became infected with WSSV after an acute salinity drop from 35 g L−1 to 10 g L−1 and lower. The mortality in shrimp, subjected to a salinity change to 10 g L−1, 7 g L−1 and 5 g L−1, was 6.7%, 46.7% and 53.3%, respectively (P