Long-Term Immune Responses and Disease Protection in Asian Seabass (Lates calcarifer) Following Sequential Nanoemulsion and Oral Hydrogel Mucosal Vaccination Against Multiple Bacterial Pathogens

Information from the abstract

Aquaculture production of Asian seabass is increasingly threatened by recurrent bacterial diseases, while practical vaccination strategies that provide protection against bacterial challenges involving multiple pathogens during extended grow-out periods remain limited. This study evaluated the immunological and protective effects of a sequential mucosal vaccination strategy in juvenile Asian seabass (Lates calcarifer; 200 fish per treatment, distributed among four replicate tanks of 50 fish) against four major bacterial pathogens: Flavobacterium covae, Vibrio harveyi, Vibrio vulnificus, and Photobacterium damselae. The vaccination regimen consisted of two nanoemulsion-based immersion vaccination events administered 14 days apart, followed by three oral chitosan–alginate hydrogel vaccination courses administered for 7, 5, and 3 consecutive days. Bacterial challenge experiments were conducted at three post-vaccination time points using immersion and intraperitoneal injection models. Growth performance and feed conversion were evaluated using replicate-tank means as the experimental units. Sequential vaccination did not significantly affect final body weight, weight gain, average daily gain, specific growth rate, or feed conversion ratio (p > 0.05). Vaccinated fish showed significantly higher antigen-specific IgM levels in skin mucus, intestinal mucus, and serum across the evaluated challenge conditions. Correspondingly, ighm, ighd, and ight expression was increased in the gills, skin, head kidney, and intestine, indicating enhanced immunoglobulin-associated responses in mucosal and lymphoid tissues. Full-length 16S rRNA gene sequencing showed vaccine-associated changes in gill and intestinal bacterial community composition, including a lower relative representation of several challenge-associated taxa and a higher relative representation of selected commensal-associated taxa. Vaccinated fish showed significantly higher cumulative survival following F. covae immersion, mixed V. harveyi/V. vulnificus/P. damselae immersion, and mixed-pathogen injection challenges (p < 0.05). These findings demonstrate that sequential nanoemulsion immersion priming and oral hydrogel boosting enhanced pathogen-specific humoral responses and increased immunoglobulin-gene expression. The sequential vaccination strategy improved survival following a separate Flavobacterium covae challenge and a combined Vibrio harveyi/Vibrio vulnificus/Photobacterium damselae challenge during the experimental period without adversely affecting growth. This needle-free strategy warrants further evaluation under commercial aquaculture conditions.

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Related topics: Aquaculture disease management and microbiota · Invertebrate Immune Response Mechanisms · Myxozoan Parasites in Aquatic Species