Abstract:There are a large number of microorganisms in the intestine of fish, which play an key role in maintaining host health. The fish immune system can monitor and regulate the intestinal microbial composition and maintain the homeostasis of intestinal flora. At the same time, the intestinal commensal microorganisms regulate the fish immune system, control the excessive proliferation of pathogenic microorganisms, and ensure the health of the host. This paper reviewed the progress of interactions between intestinal microorganisms and the host immune system in fish, and focusing on the host immune system sensing intestinal microbes, host immune system shaping intestinal microbiota, probiotics regulating host immunity and intestinal microbiota, etc. It is suggested that the ideal probiotics should be derived from the gastrointestinal tract of fish and the non-host derived probiotics should be carefully selected in aquaculture application. This paper would provide theoretical supports for the future researches on the development and application of intestinal functional microbes in fish.