Efficacy of inactivated Streptococcus iniae vaccine and protective effect of -(1,3/1,6)–glucan on the effectiveness of vaccine in red tilapia Oreochromis niloticus x O. mossambicus

Streptococcus iniae infections are becoming an increasing problem in aquaculture and have been reported worldwidein a variety of fish species. Our previous study showed that S. iniae infection in tilapia Oreochromis sp. and Asian sea bassLates calcarifer cause serious damage in fish farm in Thailand. To prevent streptococcosis caused by S. iniae, a formalinkilledvaccine was applied in red tilapia Oreochromis niloticus x O. mossambicus by injection, immersion and oral vaccination.At 1 week post vaccination, levels of antibody titer and some blood parameters response to different routes of administrationwere significantly different. The best disease resistance was found in the group injected with vaccine plus -(1,3/1,6)–glucan with the relative percent survival (RPS) of 95.12% followed by pure vaccine injection (RPS = 80.49%), immersion(RPS = 41.46%) and oral vaccination (RPS = 9.75%).No difference in blood parameters of tilapia after vaccination for 4 weeks was observed. However, antibody titer ofthe group received vaccine plus -(1,3/1,6)–glucan and vaccine alone were significantly higher than the other groups. RPS offish at week 4 post vaccination showed the same trend as the highest disease resistance recorded in the group injected withvaccine plus -(1,3/1,6)–glucan (RPS=76.00%) which significantly differ from vaccine alone (RPS=54.00%). Immersion andoral vaccination showed less effect on disease protection at week 4 post vaccination. The result from the present studyindicated that formalin-killed S. iniae vaccine provided excellent efficacy against S. iniae infection in tilapia by intrapertonealinjection and -(1,3/1,6)–glucan increased the effectiveness of vaccine produced from S. iniae