Diagnosticmethods such as an IF test and polymerase chain reactionamplification were reported (Nakajima & Sorimachi
1995, Nakajima et al. 1995, Kurita et al. 1998,Oshima et al. 1998). However, control measures for this disease have not been established. Recently, wereported on the effectiveness of a vaccine against RSIVD under laboratory conditions (Nakajima et al.1997). Herein, we describe the results regarding the effectiveness of the vaccine evaluated in a field trial.Materials and methods. To evaluate the vaccine,2000 red sea bream juveniles (mean body weight 6.2 g)were divided into 2 groups (vaccinated group and nonvaccinated group). For the vaccinated group, fish wereintraperitoneally inoculated with 0.1 m1 of vaccine solution made from the supernatant of RSIV-infected