Mariculture Probiotics: A Scoping Review of Research Trends, Knowledge Gaps and Opportunities.

The use of probiotics - live microorganisms - to enhance growth and prevent disease in mariculture species is an emerging alternative to conventional methods including antibiotics, vaccines and chemical intervention. While others have reviewed specific host organisms and probiotic genera, this review synthesises the scientific literature on the use of probiotics across a range of marine organisms to identify knowledge gaps and research opportunities. We identified widespread methodological heterogeneity, making direct inter-study comparisons difficult. Despite this limitation, 86% of in vivo studies documented positive outcomes following probiotic administration. Crustacean and finfish research dominates the field, encompassing 77% of the current literature, while molluscs, macroalgae and other invertebrates remain relatively understudied despite their significant ecosystem services and contribution to aquaculture. Probiotics provide multiple reported benefits to marine hosts, including increased growth and survival, and protection against pathogens. Bacillus and Lactobacillus from terrestrial environments are the dominant probiotics used across all studies, while marine-derived probiotic genera including Pseudoalteromonas, Vibrio, Phaeobacter, Shewanella, and Halomonas showed benefits across several hosts but remain relatively underutilised. Approximately 34% of publications evaluated the use of microorganisms isolated from the same host species in which the probiotics were tested. This review highlights the opportunity for further research into underutilised autochthonous probiotic genera and development of standardised research guidelines. We propose that future research should prioritise understanding probiotic mechanisms of action, and their use in rapidly expanding and understudied systems including macroalgae and molluscs, to ensure continued productivity with minimal impact on marine ecosystems.