FBS components in viral culture fluid inter- fere with the detection of specific antibody in imm unized fish. In the present study, we developed a method to elimi- nate the interference of FBS using a model of red sea bream iridovirus (RSIV) vaccine. In an experiment using yellowtail antiserum against BSA, which is a major compo- nent of FBS in cell culture media, antibodies against BSA were completely absorbed via incubation of antiserum in 50% FBS at 25°C for 1 h. In antibody detection, ELISA with the sera of yellowtail surviving RSIV-challenge, antibo- dies against RSIV were detected, but those against FBS dis- appeared via the pre-treatment of the sera. Therefore, antibodies against RSIV are effectively detected using ELISA with the pre-treatment of fish sera.