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.

Matrine, a bioactive alkaloid from Sophora flavescens, has gained attention as a phytogenic additive due to its antioxidant and immunomodulatory properties. Nevertheless, Nile tilapia (Oreochromis niloticus) is highly vulnerable to Streptococcus agalactiae infection under intensive aquaculture, leading to immune dysfunction and economic losses. This study aimed to evaluate the potential application of dietary matrine supplementation in enhancing tilapia health, growth performance, and resistance to bacterial infection. Fish were randomly assigned to four dietary treatments: control, 0.1% matrine (low dose), 0.5% matrine (medium dose), and 1.0% matrine (high dose). Blood, liver, spleen, intestine, head kidney, and muscle were sampled on days 0, week 4, and week 8 for growth, immune, and oxidative stress analyses. Subsequently, fish were challenged with S. agalactiae to evaluate immune gene expression and liver histopathology across groups. The results showed that dietary matrine supplementation significantly improved growth performance and feed conversion efficiency, enhanced nonspecific immune responses, and increased antioxidant enzyme activities. Moreover, 0.5% and 1.0% matrine markedly reduced mortality and hepatic injury after bacterial challenge. These findings indicate that matrine acts as an effective natural immunomodulator and may contribute to hepato-intestinal health, and dietary supplementation at 1.0% represents the relatively favorable inclusion level under the present conditions for improving health status and supporting sustainable Nile tilapia aquaculture.