Probiotics and Gut-Associated Lymphoid Tissue (GALT) in Fish: Mechanism, Application and Future Perspectives

The gut-associated lymphoid tissue (GALT) serves as the main immunological interface between fish and their aquatic environment, playing a central role in defense, homeostasis, and adaptation. Over the past two decades, probiotics have gained recognition as powerful tools for enhancing GALT function in teleost fish, influencing immunity, gut microbiota composition, and overall health. While previous reviews have addressed specific aspects of probiotic applications in aquaculture, a comprehensive synthesis linking immunological, microbiological, molecular, nutritional, and practical perspectives has been lacking. This review fills that gap by integrating these diverse domains into a unified analysis of probiotic-GALT interactions. Evidence indicates that probiotics promote beneficial shifts in gut microbial communities, support mucosal immunity through modulation of key immune cell populations and immunoglobulins, and contribute to improved growth and disease resistance. Despite promising results, challenges remain in translating laboratory findings into consistent field-level outcomes, particularly regarding strain stability, delivery methods, and host-specific responses. Future research should prioritize standardized evaluation protocols, advanced formulation technologies, and sustainable implementation strategies. By bridging disciplinary boundaries, this review provides a foundation for optimizing probiotic use to advance fish health and sustainable aquaculture.