Efficacy and safety of a live vector vaccine against iridovirus in large yellow croaker (Larimichthys crocea).

Large yellow croaker iridovirus (LYCIV) is a causative agent of viral disease in large yellow croaker (Larimichthys crocea, LYC), causing high mortality rates and substantial economic losses in modern aquaculture. To address the need for effective prevention and control strategies, this study developed a safe and efficacious recombinant vaccine incorporating the coding region of the LYCIV major capsid protein (MCP) gene. Juvenile LYCs were immunized through immersion, the expression levels of the LYCIV MCP gene and several representative immune-related genes were measured, and the relationship between viral gene expression and host immune responses was explored. In addition, serum antibody levels and the protective efficacy of the vaccine against LYCIV challenge were assessed. The considerable upregulation of the LYCIV MCP gene and all tested immune-related genes in vaccinated fish, implying that heightened immune responses are associated with increased viral gene expression. Moreover, vaccinated fish exhibited a gradual increase in LYCIV antibody production, in contrast to the control group. The recombinant live vector vaccine conferred strong protective efficacy, achieving a relative percent survival of 64.52% following viral challenge. Overall, these findings indicate that the live vector vaccine provides robust protection against LYCIV infection. Furthermore, the replication-defective adenovirus employed as the vector represents a promising platform for the development of fish vaccines. This study contributes new insights into live vector vaccine development and offers a practical strategy for the prevention and control of iridovirus outbreaks in LYC aquaculture.