4. DiscussionThe first killed vaccine was developed to prevent trout lossescaused by S. iniae infection [28]. Killed vaccines are generallyadministered through injection to achieve high efficacy. Previousresearch demonstrated that bath immunization of tilapia resultedin RPS values that were 2-fold lower than those achieved usingi.p. vaccination [29]. In a field trial, Eldar et al. [28] reported thatthe mortality of rainbow trout intraperitoneally immunized witha formalin-killed S. iniae vaccine was 5%, but exceeded 50% innon-immunized rainbow trout. Similarly, the results of this studydemonstrated that i.p. injection of a formalin-killed S. iniae vaccineprovides a higher level of protection in groupers (RPS, 97.5%–100%)after S. iniae challenge; such a vaccine can provide excellent efficacyagainst S. iniae infection in fish.Oil-based vaccines administered to fish provide long-term pro-tection [30]. In this study, we posit that whether antigens are mixedwith the ISA763A or AS-F adjuvant, adequate protection is achievedin the vaccinated groupers. Protection conferred by the tested vac-cine lasted a minimum of 6 months, as determined in the laboratorychallenge. As streptococcosis poses a threat to groupers during thesummer