Medicinal and Aromatic Plant Oils in Aquafeeds: Mechanistic Perspectives on Growth Promotion, Immunomodulation, and Stress Resilience

The aquaculture industry is increasingly transitioning toward sustainable aquafeeds, driven by the economic and environmental necessity to replace marine-derived fishmeal and fish oil with plant- and insect-based alternatives. This nutritional shift introduces physiological challenges, accelerating the search for natural, sustainable functional additives. The primary goal of this review is to comprehensively evaluate the application of medicinal and aromatic plant oils (MAPOs) in aquafeeds, providing mechanistic perspectives on their roles in growth promotion, immunomodulation, and stress resilience. We synthesize current literature to link MAPO chemical composition, particularly phenolic monoterpenes and phenylpropenes, with biological responses, advanced delivery systems, and metabolic pathways. Key findings demonstrate that MAPOs can effectively stimulate appetite, modulate the gut microbiome, and enhance antioxidant defenses via the Nrf2-Keap1 pathway, thereby improving disease resistance. However, a critical limitation in the current literature is the high variability and inconsistent outcomes reported across different aquatic species and developmental stages. These discrepancies are largely attributed to strong chemotypic variability of essential oils, unstandardized extraction protocols, and dose-dependent responses that can sometimes yield neutral or suppressive effects. To successfully transition MAPOs from experimental trials to reliable commercial applications, future research must prioritize standardized dose-response evaluations, address species-specific variability, and utilize advanced formulation technologies such as nanoemulsions.