Postbiotics and Paraprobiotics as Next-Generation Gut Microbiome Modulators in Sustainable Aquaculture Health.

Widespread antibiotic use in aquaculture has increased selective pressure on resident bacterial communities, accelerating the emergence of resistance in key pathogens and raising concerns for animal health, environmental microbiomes, and food-chain safety. Reducing dependence on therapeutic antimicrobials requires alternative strategies that remain effective under the processing and biosafety constraints of intensive production systems, where recurrent bacterial diseases continue to cause substantial economic losses. Live probiotics, currently the most extensively studied microbiome-based intervention, have practical limitations, including reduced viability during feed pelleting and extrusion, transient gut colonization, strain-specific host responses, biosafety concerns related to horizontal transfer of antimicrobial-resistance genes, and variable regulatory requirements across regions. Postbiotics, defined as preparations of non-viable microbial biomass, with or without metabolites, that confer a demonstrated health benefit in the target host, and paraprobiotics, which emphasize inactivated whole-cell preparations that preserve surface-associated microbial molecular patterns, may help address several of these constraints. These approaches offer improved compositional definition, greater feed-processing stability, and a potentially more favorable biosafety profile. Because they are non-viable, their anti-pathogen effects do not depend on growth or competitive colonization but may instead involve preformed antimicrobial compounds retained in some preparations, interference with pathogen attachment, modulation of the intestinal environment, reinforcement of barrier function, and stimulation of host immune responses. This review synthesizes current evidence on postbiotics and paraprobiotics in aquaculture, with emphasis on structural classification, pattern-recognition receptor signaling, intestinal barrier function, innate immune priming, encapsulation technologies, and translational readiness. Taken together, available evidence supports postbiotics and paraprobiotics as promising, but not yet fully characterized, alternatives to live probiotics within antibiotic-reduction strategies for aquaculture. Progress toward commercial application will depend on resolving key questions related to dose-response relationships, processing stability in formulated feeds, and species-specific efficacy.