Integrated field vaccination and laboratory challenge reveal immune gene responses and protective efficacy in Asian seabass (Lates calcarifer) following oral administration of an inactivated Vibrio harveyi vaccine

Vibriosis, caused by Vibrio spp., poses a significant challenge in marine aquaculture, leading to severe economic losses. Vaccination has emerged as a safer and more effective alternative to antibiotics for disease control, with oral vaccination offering advantages such as ease of administration and scalability for large-scale aquaculture operations. This study evaluated the efficacy of an oral inactivated Vibrio harveyi vaccine in a field environment with cage-cultured Asian seabass (Lates calcarifer) at Pulau Ketam, Klang, Selangor, Malaysia. Fish were divided into two groups: (1) a vaccinated group fed a commercial diet supplemented with formalin-killed V. harveyi (108 CFU/mL) and palm oil as an adjuvant and (2) a placebo control group fed a commercial diet supplemented with phosphate-buffered saline (PBS) and palm oil adjuvant. The vaccine was administered orally at weeks 0, 2, and 6 for three consecutive days at a dosage of 4% of the fish’s body weight. Immune-related gene expression, including dendritic cells (DCs), complement factor 3 (C3), chemokine ligand 4 (CCL4), tumor necrosis factor-α (TNF-α), and immunoglobulin-T (IgT), was significantly upregulated (p < 0.05) in vaccinated fish compared to controls, with peak expression observed following booster doses. At week 10, a laboratory challenge trial with V. harveyi (1 × 108 CFU/mL) demonstrated an 80% relative percentage survival (RPS) in the vaccinated group, whereas the unvaccinated group exhibited 100% mortality. In addition, vaccinated fish displayed reduced clinical signs following infection. These findings highlight the potential of oral inactivated V. harveyi vaccines to induce robust immune responses and confer effective protection against vibriosis in Asian seabass. This approach provides a practical and scalable solution for disease management in marine aquaculture, improving health outcomes and productivity for fish farmers.

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