Effects of probiotics, prebiotics, and synbiotics on immune function, disease resistance, digestive health, and stress management in fish culture

Aquaculture is a fast-growing farming sector, and fish production aims to meet global nutrient demand. Aquatic organisms are directly exposed to deteriorated ecological environments and die during outbreaks. In the beginning of aquaculture, several synthetic drugs were introduced to protect organisms, and continuous exposure results in antibiotic accumulation in fish and the development of drugresistance among microorganisms. In addition, exposure to these antibiotics affects the environment and affects nontargeted organisms. Probiotics, followed by prebiotics, were introduced in the aquaculture industry, and synbiotic interventions were subsequently proposed. Synbiotics are active combinations of prebiotics and probiotics that are used to improve digestive enzyme activity, antioxidant enzymes, antioxidant chemicals, immunity, growth performance, and feed utilization efficacy in fish. The application of synbiotics improved overall fish growth, stress mitigation and improved yield in aquaculture. Prebiotics, probiotics, and synbiotics are considered alternatives to synthetic drugs. Synbiotics improved gut microbiota, immune response, antioxidant mechanism, and stress mitigation effects. This narrative review focuses on current research advancements to address the research gap between synbiotics and healthy fish production. The variations in standard methodology in feed formulation, dosage of synbiotics, stages of fish, treatment period, route of administraton, selected fish type, and environmental conditions, and effectiveness of synbiotics have contributed to the major complexities of the field. The present study aimed to summarize the current research on the effects of probiotics, prebiotics, and synbiotics on antioxidant molecules, digestive enzymes, and stress mitigation effects in fish, shrimps and oysters. From these results, it can be found that fish have the potential to change their microbial community according to the surrounding environment. Identifying research gaps in this field and understanding the role of synbiotics can improve fisher-friendly strategies to maximize fish growth performance, the immune response, and ecological balance.