Functional nutrition plays a pivotal role in aquaculture by promoting fish growth, enhancing immune responses, and mitigating the impact of environmental and pathogenic stressors. With the intensification of fish farming and growing concerns over antibiotic resistance, the use of functional feeds including nutraceuticals, prebiotics, probiotics, antioxidants, and immunostimulants has emerged as a sustainable alternative to conventional practices. This review critically examines the nutritional requirements of fish, explores the bio efficacy of various feed additives, and evaluates their roles in gut health modulation, disease resistance, and stress mitigation. We also discuss proactive health management strategies and the integration of vaccination and feed-based interventions. The review highlights current advancements, identifies research gaps, and emphasizes the need for precision in formulating functional feeds tailored to species-specific requirements. This integrated nutritional approach supports healthier fish stocks, improves aquaculture productivity, and reduces the industry's ecological footprint.