A Novel Postbiotic Product Based on IWeissella cibaria/I for Enhancing Disease Resistance in Rainbow Trout: Aquaculture Application

Antibiotics have become a threat to aquaculture due to their negative impact on aquatic environments, fish, and consumers. To contribute to the research and creation of novel tools that are able to treat and control disease in fish and substitute the use of antibiotics in the aquaculture industry, this study investigates the impact of postbiotics added through feed on health parameters and disease resistance in rainbow trout. After 30 days of supplementation with postbiotics, an improvement in survival rate when facing an experimental infection with the causative agent of Red Mouth Disease was observed in rainbow trout. This research illustrates, for the first time, the positive effect of postbiotic supplementation on rainbow trout survival when challenged with Red Mouth Disease infection; in summary, this proves the suitability of the postbiotic product for the aquaculture industry and its relevance regarding the current efforts to reduce and replace the utilization of antibiotics in animal husbandry. Postbiotics are innovative tools in animal husbandry, providing eco-friendly solutions for disease management within the industry. In this study, a new postbiotic product was evaluated for its impact on the health of rainbow trout (Oncorhynchus mykiss). In vivo studies were conducted to assess the safety of the Weissella cibaria strains used in postbiotic production. Additionally, this study evaluated the impact of diet supplementation with 0.50% postbiotics on growth performance during a 30-day feeding trial; the gut microbial communities, immunomodulation, and protection against Yersinia ruckeri infection were evaluated. The strains did not harm the animals during the 20-day observation period. Furthermore, the effect of postbiotics on growth performance was not significant (p < 0.05). The treated group showed a significant increase in acid-lactic bacteria on the 30th day of the feeding trial, with counts of 3.42 ± 0.21 log CFU/mL. Additionally, there was an up-regulation of the pro-inflammatory cytokine IL-1β in head kidney samples after 48 h of feed supplementation, whereas cytokines IL-10, IL-8, INF-γ, and TNF-α were down-regulated. The findings indicate that rainbow trout fed with postbiotics saw an improvement in their survival rate against Y. ruckeri, with a 20.66% survival improvement in the treated group. This study proves that incorporating postbiotics from two strains of W. cibaria previously isolated from rainbow trout into the diet of fish has