A simple and easy method of concentrating white spot syndrome virus by employing aluminium sulphate, alum as a flocculant was developed and evaluated for field detection. The concentrated virus was detected by a monoclonal antibody based flow-through assay, RapiDot and compared its performance with polymerase chain reaction. The semi-purified virus that was flocculated by 15 and 30 ppm alum in a 50 ml cylinder can be detected successfully by both RapiDot and I step PCR. In addition, alum could also flocculate the virus that is detectable by II step PCR and the concentration of virus was similar to the one observed in water from an infected pond. Furthermore, experimental infection studies validated the successful concentration of virus by alum flocculation followed by rapid detection of virus using monoclonal antibody based RapiDot. Overall, the results obtained in this study indicate that the white spot syndrome virus in water could be easily flocculated by alum for sensitive field detection by monoclonal antibody based RapiDot.