Agricultural Research,Education and Extension Organization Iranian Journal of Fisheries Sciences 1562-2916 24 4 2025 07 01 An inactivated bivalent vaccine effectively protects Asian sea bass (Lates calcarifer) against Streptococcus iniae and Vibrio harveyi infections 863 885 134005 10.22092/ijfs.2025.134005 EN M. Kahkesh Department of Clinical Sciences Faculty of Veterinary Medicine, Shiraz University, Shiraz, Iran M. Alishahi Department of Livestock, Poultry and Aquatic Animals Health, Faculty of Veterinary Medicine, Shahid Chamran University of Ahvaz, Ahvaz, Iran S. Soltanian Department of Clinical Sciences Faculty of Veterinary Medicine, Shiraz University, Shiraz, Iran A. Gholamhoseini Department of Clinical Sciences Faculty of Veterinary Medicine, Shiraz University, Shiraz, Iran M. Ghorbanpoor Department of Pathobiology, School of Veterinary Medicine, Shahrekord University, Shahrekord, Iran A. Yektaseresht Department of Pathobiology, Faculty of Veterinary Medicine, Shiraz University, Shiraz, Iran. Journal Article 2025 07 15 Co-infection with <em>Streptococcus</em> <em>iniae</em> and <em>Vibrio harveyi </em>is the major health challenge in Asian sea bass (<em>Lates calcarifer</em>) farms. Vaccination is the most effective means of preventing these diseases, therefore, this study presents an efficacious bivalent vaccine against <em>S. iniae </em>and<em> </em><em>Vibrio harveyi</em> infections in Asian sea bass. 420 juvenile sea bass (weighing 20.35 ± 0.37 g) were separated into seven equal groups in triplicates: group A: received Phosphate-buffered saline as a control group, groups B and E: immunized with <em>S. iniae</em> vaccine via injection (<em>S.i</em>-Inj) and immersion (<em>S.i</em>-Im) routes, groups C and D: immunized with <em>V. harveyi</em> vaccine via immersion (<em>V.h</em>-Im) and injection (<em>V.h</em>-Inj) routes, and groups F and G: immunized with bivalent <em>S. iniae</em>+<em>V. harveyi</em> vaccine via immersion (Bi-im) and injection (Bi-inj) routes. The blood, serum, and gene samples were taken on 0, 30, and 60 days of the experiment and to measure specific and non-specific immune parameters, hematological and immune-related gene expression. The bacterial challenge test was used as a protective immunity measure at the end of the experiment. The results showed that the injection bivalent vaccine (<em>S. iniae+V. harveyi</em>) route was more effective than monovalent vaccines in enhancing the specific (antibody titer) and non-specific (lysozyme and complement activity, Nitro Blue Tetrazolium (NBT) reduction, protein, and globulin level) immune responses. Meanwhile, the vaccine efficacy and expression of <em>IL-10</em> and <em>GM-CFC</em> genes in the bivalent vaccine were significantly higher (<em>P<0.05</em>) than monovalent vaccines. These results indicate that the high immunogenicity and protective immunity provided by the bivalent vaccine (<em>S. iniae+V. harveyi</em>) strongly support its use as a general preventive measure against streptococosis and vibriosis in Asian sea bass farms. https://jifro.areeo.ac.ir/article_134005_793ec49a8d7bbdf16f3e7581daa75b8c.pdf