EFFECTS OF PEANUT PEEL EXTRACTS AS FUNCTIONAL ADDITIVES FOR EUROPEAN SEABASS (Dicentrarchus labrax) JUVENILES

As aquaculture continues to expand as a major provider of animal protein worldwide, integrating circular economy principles is becoming increasingly important to reduce waste, add value to by-products, and promote more sustainable production systems. The incorporation of functional additives into aquafeed to mitigate physiological responses to common aquaculture stressors, such as handling, overcrowding, and netting, has gained attention in recent years, especially given the context of climate change and the urge for more sustainable aquatic food production. In this thesis, novel peanut peel extracts were obtained using natural deep eutectic solvents (NADES) and ethanol, combined with microwave-assisted extraction, to enhance the yield of phenolic and antioxidant compounds. Five experimental diets were formulated: a control, two diets including ethanolic extracts at different inclusion levels (ET1 and ET2), and two with NADES extracts (NADES1 and NADES2). The diets were evaluated in a 4-week feeding trial on European seabass (Dicentrarchus labrax) juveniles, followed by a one-week thermal stress trial (32°C) in a recirculating aquaculture system (RAS). Growth variables, oxidative stress markers in liver and muscle sampled after the feeding trial and after the thermal stress trial, as well as survival rates during the thermal stress trial, were assessed. The study showed that peanut peel supplementation did not impair growth performance compared to the control diet. Diets containing ethanol extracts tended to reduce feed and protein efficiency ratios, while those with NADES extracts maintained performance. Following the feeding period, ET diets induced higher hepatic superoxide dismutase activity without parallel increases in catalase or glutathione peroxidase, suggesting partial oxidative imbalance, whereas NADES diets indicated steadier antioxidant protection. After thermal stress, muscle lipid peroxidation was significantly lower in fish fed the ET1 diet, while survival rates improved markedly with the ET2 diet (+33%) and the NADES diets (+25%) compared to the control diet. In conclusion, peanut peel extracts can be used as a natural functional additive to reduce oxidative stress and enhance the resilience of European seabass in aquaculture, contributing to the development of sustainable strategies for fish health management.