The size of fish at vaccination appears to play an important role in S. agalactiae vaccination by IP injection, but not by bath immersion. Larger IP vaccinated tilapia had lower mean percent mortalities than smaller IP vaccinated tilapia and than both large and small tilapia vaccinated by bath immersion. In contrast, Klesius et al. [11] did not find any association between tilapia age and/or size and S. iniae vaccine efficacy. Longer duration of vaccination before challenge and/or maintenance of fish at a lower water temperature did not appear to affect IP vaccine efficacy