Effect of Dietary Supplementation with Red-Fleshed Dragon Fruit (Hylocereus polyrhizus) Juice By-Product Extract (HJBE) on Growth Performance, Digestive Enzyme Activity, Antioxidant Status, Immune Parameters, and Disease Resistance Against Edwardsiel

This study investigated the effects of dietary supplementation with <i>Hylocereus polyrhizus</i> juice by-product extract (HJBE) on growth performance, digestive enzyme activity, antioxidant status, immune response, and disease resistance against <i>Edwardsiella tarda</i> in juvenile <i>Pagrus major</i>. The HJBE, prepared from juice-processing residues, contained measurable levels of bioactive compounds, including vitamin C, total phenolics, and flavonoids, and exhibited noticeable antioxidant activity. Five experimental diets containing 0 (control), 0.5, 1.0, 2.0, and 3.0 g/kg HJBE were fed to juvenile red seabream (initial weight of 7.0 ± 0.01 g) for eight weeks. Fish fed the diet containing 1.0 g/kg HJBE (HJBE1) showed significantly higher final weight, weight gain, specific growth rate, feed efficiency, and protein efficiency ratio compared with other groups. Trypsin activity in intestine was also significantly enhanced in the HJBE1 group, suggesting improved feed utilization. Whole-body composition and hematological indices did not differ among treatments. Plasma antioxidant parameters showed a dose-dependent trend, with catalase and glutathione levels lower at inclusion levels of 0.5-1.0 g/kg. Serum lysozyme activity and immunoglobulin M concentrations were significantly higher in fish fed HJBE1 compared to the controls, corresponding to improved survival after <i>E. tarda</i> challenge. These findings suggest that even moderate levels of bioactive compounds in HJBE can beneficially influence antioxidant homeostasis, immune defense, and growth performance. In conclusion, dietary inclusion of 1.0 g/kg HJBE effectively improved growth, digestive physiology, antioxidant balance, and disease resistance in juvenile <i>P. major</i>.