Bacteriophages in the fish mucosa: updates on their biology, interactions, and applications

The alarming increase in resistance of several pathogenic bacteria that infect humans resulted in existing antibiotics losing efficacy. Similarly, the aquaculture industry is facing the same problem with antibiotics being administered to fish to maintain their health. There is a need for new approaches to combat these pathogens, and currently, bacteriophages are revisited by scientists to be used as alternatives for antibiotics. Bacteriophages hijack the bacterial cell to replicate themselves and proliferate. Mucosa, an integral part of the innate immunity of fish, is abundant with phages, and the tripartite interaction among phages, bacteria, and the host is gaining attention to understand fish health. Most phages exhibited activity against pathogenic bacteria that are associated with the fish mucus. Studies demonstrated that phages have adaptations to the mucosal environment and have specificities to fish mucosal bacteria, minimizing the negative effects of bacterial pathogens. Some of the bacterial pathogens targeted by the phages in this review are also able to infect humans. A comprehensive discussion on the use of phages in aquaculture as a treatment approach for various diseases caused by bacteria is presented, along with their advantages and limitations of their applications. The future trajectory of this field of study is also discussed in relation to effective management of fish health in aquaculture.