The white leg shrimp Litopenaeus vannamei has been converted commercially into the most predominant cultivated shrimp species in the world. However, such shrimp’s intensive farming worldwide propitiates outbreaks of epizootic diseases, primarily of viral etiology. In the principal Brazilian region of shrimp production, it is known that a reduction in the salinities of culture ponds causes the appearance of viral diseases. In the present work, we investigate the replication of the infection myonecrosis virus (IMNV) in controlled levels of salinity during the first 12 hours of infection. Using quantitative real-time PCR and statistical analysis, we verify that low salinity positively facilitates IMNV replication and proliferation by decreasing the generation time from 57.4 min (at 35 g L-1, optimum salinity) to 25.2 min at (5 g L-1, stressing concentration). Similarly, a positive relationship was demonstrated between a decrease in salinity and the reduction in the generation time of persistent infectious hypodermal and hematopoietic necrosis virus, a virus that usually co-infects shrimp in farm ponds.