Pacific white shrimp, 10-15 g in body weight, were purchased from a local shrimp farm and tested for the presence of WSSV by PCR to ensure that they were WSSV-free. Shrimp of each group were stocked in 100-L aquaria of sand-filtered , ozone-treated and flow-through salt water at 22-25°c, They were acclimated to the laboratory conditions for 7 days and fed with commercial or treated at 5% of body weight per day before and during the experiments