Plant-Derived Dietary Antioxidants for Mitigating Oxidative Stress in Cultured Fish: Mechanisms, Experimental Evidence, and Practical Limitations

Oxidative stress is an important concern in cultured fish because environmental, nutritional, and physiological challenges can disturb cellular redox regulation and contribute to molecular damage. Plant-derived dietary antioxidants have been investigated as potential feed additives to support antioxidant defenses and improve fish health. This narrative review examines major plant-derived antioxidant compounds and preparations, their proposed mechanisms of action, experimental evidence from finfish feeding trials, and limitations affecting their practical application. Relevant publications were evaluated through a targeted narrative approach, with emphasis on antioxidant enzyme activities, oxidative damage indicators, growth, immune responses, and stress tolerance. Feeding trials have reported changes in superoxide dismutase, catalase, glutathione-related indicators, and malondialdehyde following supplementation with selected plant-derived compounds and ingredients. However, responses were not uniform across studies. Some treatments reduced lipid peroxidation without increasing antioxidant enzyme activities, whereas others changed enzymatic defenses without significantly affecting malondialdehyde. Improvements in growth or disease-related outcomes were also not consistently associated with reduced oxidative damage. These differences were influenced by ingredient preparation, dietary inclusion level, fish species, and experimental conditions. Practical application is further complicated by variation in ingredient composition, losses of active compounds during feed processing, uncertain bioavailability, and limited information on long-term safety and commercial-scale performance. The available evidence indicates that selected plant-derived dietary antioxidants may support oxidative stress management under specific conditions, but their effectiveness cannot be generalized across ingredients or fish species. Future investigations should integrate ingredient characterization, appropriate dose evaluation, feed-processing stability, and complementary indicators of oxidative damage to establish more reliable recommendations for aquaculture feeds.