The relative percentage survival (RPS, Amend, 1981) was also determined by the formula RPS =
[l - (% loss of immunized fish/% loss ofl. controls)] X 100. To detect viral antigen, 10 survivors were randomly sampled in
each group. Then, the spleens were removed from the fish and the presence of RSIV-specific antigens was determined
by means of an IF test. body weight Of loo fish randomly sampled from each group was also determined 6 and 12 wk post vaccination