Introduction
Postbiotics are preparations of inanimate microorganisms and/or their components that confer a health benefit on the host. They include microbial structures and metabolites such as organic acids, peptides and bacteriocins, all contributing to biological functionality. In aquaculture, the need for feed-additives that are stable during production, safe to handle and effective across species is increasing. At the same time, cultured aquatic animals are exposed to multifactorial challenges, including pathogens, environmental stress and gut health disturbances. This requires solutions acting via multiple biological pathways. This study aimed to characterise the modes of action of a postbiotic using complementary in vitro, ex vivo and in vivo approaches.
Materials and methods
In vitro antibacterial activity was assessed using co-cultivation assays with industry burdening aquatic pathogens including Vibrio, Aeromonas, Yersinia and Streptococcus species. Cell-free supernatant (CSF) was used to isolate the effects of soluble components. An ex vivo intestinal explant model was applied to the final product and the CFS to evaluate immune and barrier responses through cytokine expression (IL-1β, IL-8, TNFα, IL-10) and tight junction markers (occludin, claudins) and to confirm previous in vitro observations of the same readouts in other cellular models. In vivo trials across aquaculture species evaluated robustness under pathogenic and environmental challenges.
Results and discussion
The postbiotic additive showed broad antimicrobial activity, indicating direct suppression of pathogens via soluble bioactive compounds. Ex vivo results demonstrated activation of innate immune pathways with concurrent upregulation of IL-10, suggesting balanced immune modulation with anti-inflammatory control. Increased expression of tight junction markers indicated improved epithelial integrity, consistent with enhanced barrier function and reduced permeability. In vivo trials confirmed improved resilience under challenge conditions, reflecting the integration of antimicrobial, immune and barrier effects. These complementary mechanisms are relevant across aquaculture systems, where animals face overlapping stressors.
Conclusion
Postbiotics act through interconnected mechanisms including pathogen inhibition, modulation of inflammatory responses and reinforcement of intestinal barrier function. Their stability and compatibility with feed production make them promising functional additives for aquaculture. The consistency of responses across experimental models indicates that their benefits are not species-specific but represent general physiological pathways. Postbiotics therefore offer a versatile and scalable solution to support health and performance across aquaculture species and production systems.