From waste to wellness: Citrus by-products as nutritional and immunological enhancers in aquaculture

The aquaculture industry plays a vital role in global protein supply; however, it faces significant challenges, including escalating feed costs, disease outbreaks, and concerns over environmental sustainability. Citrus by-products offer a valuable and underutilized renewable resource for developing functional aquafeeds. Green extraction technologies, particularly ultrasound-assisted extraction, have demonstrated high efficiency in recovering bioactive compounds, increasing phenolic yields by more than 30% while substantially reducing solvent consumption. The inclusion of citrus-derived bioactive in aquafeeds enhances growth performance, immune function, and disease resistance in aquatic species. For example, dietary supplementation with lemon peel extracts improved survival in Nile tilapia to over 80%, while bitter orange essential oil increased growth rate and modulated immune-related gene expression in common carp. Despite these promising results, bioavailability, metabolic pathways, and species-specific responses remain insufficiently understood. This review synthesizes advances in green extraction and functional applications of citrus bioactives, identifying critical research gaps to guide sustainable aquaculture innovation. • Citrus by-products enhance fish growth, immunity, and disease resistance. • Essential oils from citrus peels improve metabolic regulation in fish. • Green extraction technologies can efficiently extract bioactive compounds from citrus waste. • Citrus-derived pectin, oils, and phenolics improve fish health, with focus on mechanisms. • Citrus by-products support sustainable aquaculture by reducing waste and enhancing fish performance.