Tilapia, as one of the fish widely cultured around the world, is suffering severe impact from the streptococcus disease with the deterioration of the breeding environment and the increasing of breeding density, which brings serious economic loss to tilapia farming. In this study, the surface immunogenic protein (Sip) of Streptococcus agalactiae (S. agalactiae) was selected as the potential candidate antigen and connected with bacterial nano cellulose (BNC) to construct the nanocarrier subunit vaccine (BNC-rSip), and the immersion immune effects against S. agalactiae and Streptococcus iniae (S. iniae) in Nile tilapia were evaluated on the basis of the serum antibody level, non-specific enzyme activity, the immune-related gene expression and relative percent survival (RPS). The results indicated that Sip possessed the expected immunogenicity according to the immunoinformatic analysis. Compared with the rSip group, BNC-rSip significantly induced serum antibody production and improved the innate immunity level of tilapia. After challenge, the RPS of BNC-rSip groups were 78.95% (S. agalactiae) and 67.86% (S. iniae), which were both higher than those of rSip groups,31.58% (S. agalactiae) and 35.71% (S. iniae), respectively. Our study indicated that BNC-rSip can induce protective immunity for tilapia through immersion immunization and may be an ideal candidate vaccine for controlling tilapia streptococcal disease.

Acute phase response related molecules are a class of proteins whose concentration changes rapidly and significantly in response to abnormal conditions such as injury, infection, and inflammation. The levels of acute phase response related molecules can reflect abnormalities in the body, but related studies in teleost fish are still relatively limited. In this study, Cp, Hap, Hep, Hx, IL-1β, and IL-6 of largemouth bass (Micropterus salmoides) were identified, the spatiotemporal dynamics of these six acute phase response related molecules in blood, liver, spleen, and brain tissues of largemouth bass before and after infection with Streptococcus agalactiae were analyzed, and they were compared and analyzed for their potential use as indicators to detect S. agalactiae infection. The results showed that in healthy largemouth bass, the distribution of acute phase response related molecules (except IL-6) was highest in the liver. All the examined genes exhibited significant changes in their transcription levels across the tested tissues after infection. Furthermore, most genes exhibit higher expression levels in the spleen compared with other tissues. Hep and IL-1β genes in spleen tissue and Hx and IL-6 in brain tissue showed significant increase from 0 to 72 h post infection (hpi) compared with the control group. Among these, IL-1β is the only acute phase response related molecule whose expression levels were more than 150-fold, reaching 165-fold to 270-fold from 6 to 24 h post infection in the spleen. This study explores the temporal correlation between several acute phase response related molecules and streptococcal infection in largemouth bass, providing insights and references for subsequent research on early infection response proteins.