Abstract
Infectious diseases remain a persistent and costly challenge in Atlantic salmon (Salmo salar) aquaculture, contributing to mortality rates, compromised animal welfare, and economic losses. Central to the first line of defense of the host are mucosal surfaces which are the gills, skin, and gut, serving as a critical immunological interface with the external environment. These barriers are not only sites of pathogen entry but also hubs of complex host-microbiota-pathogen interactions that can determine infection outcomes. Consequently, strategies that modulate mucosal microbiota, such as probiotic administration, have gained growing attention. This study critically examined the current body of evidence on the microbiota composition in healthy salmon and modulation via the application of probiotics to reinforce mucosal barrier function and microbiome resilience in salmon. Probiotic strains, including Pediococcus acidilactici, Carnobacterium spp., and Lactococcus lactis, have demonstrated protective effects through competitive exclusion, enhancement of innate immunity, and reduction of pathogen load in challenge experiments. However, findings across studies often diverge due to strain-dependent effects and lack of consistency in experimental designs, highlighting a need for more harmonised methodologies. A significant bottleneck in the field is the limited and inconsistent use of microbial profiling tools such as 16S rRNA gene amplicon sequencing, making cross-study comparisons difficult and potentially hindering progress toward evidence-based probiotic application. Despite promising results, significant knowledge gaps remain regarding the mechanisms of action, host-microbe interactions, long-term impacts, and the lack of standardised protocols for probiotic research in salmon. Addressing these gaps will be essential for developing robust, evidence-based probiotic interventions for disease management in Atlantic salmon farming.
Keywords: mucosal microbiome, disease management, aquaculture health and welfare