In recent years, aquaculture business in the world has been rapidly developed. Viral pathogens especially White Spot Syndrome Virus (WSSV) causes huge economic losses to aquaculture companies. Every were 100% cumulative mortality were observed in all species of cultured shrimps due to WSSV infection. To treat WSSV, several antiviral compounds obtained from both terrestrial as well as aquatic plants were tested, some of them have act as good antiviral activity and some act as immunostimuants. In the same series, we tested the antiviral potency of marine red algae Hypnae spinella against WSSV. The antiviral activity of crude methanolic extract of H. spinella were analysed in vivo in freshwater crabs Paratelphusa hydrodomous. Bio-assay showed strong activity against WSSV and results were confirmed by histopathology and DNA polymerase chain reaction. © 2014, Sphinx Knowledge House. All rights reserved.