Significantly higher protective effects were observed in the actively vaccinated fish, as previously demonstrated [5e8]. However, a higher percentage of mortalities was observed in these fish than expected based on this prior research, but this can be attributed to the observed severe aggression among tankmates. Even so, fish actively vaccinated with the S. agalactiae vaccine [5] exhibited a significant increase in specific antibody levels over 90 d, and these levels were roughly similar to those found in a previous S. agalactiae vaccine study [8]. As in this previous vaccine study paper, increased pre-challenge OD levels among the actively vaccinated fish were significantly correlated with post- challenge survival. The fish injected with TSB did not exhibit such an increase in antibody levels. The post-challenge specific antibody OD levels among the vaccinated and control groups did increase significantly over pre-challenge levels, but there were still significantly less mortalities among the vaccinated fish than among control fish after challenge. The ASA serum samples from these time points were used to passively immunize tilapia against S. agalactiae