Viral diseases are an important obstacle in the crustacean aquaculture industry, and white spot disease (WSD) is recognized as the most threatening one (Verbruggen et al., 2016). The first outbreak of WSD emerged in East Asia in the early 1990s and then spread rapidly into almost all major aquaculture areas worldwide, such as Europe, Americas, Australia and India (Stentiford et al., 2009;Wang et al., 2018). Nowadays, WSD outbreaks continue to occur, result in tremendous production and economic losses and severely hinder the development of global crustacean aquaculture. White spot syndrome virus (WSSV) as the etiological agent of WSD can

The disease caused by Micropterus salmoides rhabdovirus (MSRV) has brought substantial economic losses to the largemouth bass aquaculture industry in China. Vaccination was considered as a potential way to prevent and control this disease. As a kind of sustained and controlled release system, alginate and chitosan microspheres (SA‐CS) are widely used in the development of oral vaccination for fish. Here, we prepared a king of alginate‐chitosan composite microsphere to encapsulate the second segment of MSRV glycoprotein (G2 protein) and then evaluated the immune effect of the microsphere vaccine on largemouth bass. Largemouth bass were vaccinated via intragastric immunization by different treatments (PBS, SA‐CS, G2 and SA‐CS‐G2). The results showed that a stronger immune response including serum antibody levels, immune‐related physiological indexes (acid phosphatase, alkaline phosphatase, superoxide dismutase and total antioxidant capacity) and the expression of immune‐related gene (IgM、IL‐8、IL‐1β、CD4、TGF‐β、TNF‐α) can be induced obviously with SA‐CS‐G2 groups compared with G2 groups when fish were vaccinated. Furthermore, fish were injected with a lethal dose of MSRV after immunization for 28 days, and the highest relative percentage survival (54.8%) was observed in SA‐CS‐G2 group (40 μg per fish), which is significantly higher than that of G2 group (25.8%). This study showed that alginate‐chitosan microspheres as the vaccine carrier can effectively improve the immune effect of oral vaccination and induce better immune protection effect against MSRV infection.