Ellagic Acid and Pomegranate ( Punica granatum ) Peel Powder Enhances Growth and Health Performance in Nile Tilapia ( Oreochromis niloticus )

Ellagic acid (EA), in pure form or extracted from pomegranate ( Punica granatum ) peel (PP), is a bioactive polyphenol that provides strong anti‐inflammatory and antioxidant effects in cultured fish. To investigate the benefit and any adverse effects of PP as a source of EA, and pure EA by assessing growth parameters, digestive enzymes, antioxidant, and immune factors when supplied to 450 juvenile Oreochromis niloticus (10.4 ± 0.9 g) over 60 days. Feeding treatments used a standard feed with EA included at three concentrations (i.e., 0.1, 0.15, and 0.2 g kg −1 ) and PP at three concentrations (i.e., 10, 15, and 20 g kg −1 ) and in combination with similar doses (i.e., EP 1 = 50 mg + 5 g kg −1 , EP 1.5 = 75 mg + 7.5 g kg −1 , and EP 2 = 100 mg + 10 g kg −1 to keep the EA content around 0.1, 0.15, 0.2 g kg −1 , respectively) as well as a control without inclusion. The final weight (FW) of the fish was significantly increased in most treatments compared to the control group ( p < 0.05). White blood cell (WBC) counts increased in higher dose treatments for both EA and EP (i.e., EA 0.2 g, EP 1.5, and EP 2). Antioxidant and key digestive enzyme (protease, lipase, and α ‐amylase) activities were generally elevated, with most treatments showing significant ( p < 0.05) increases in the transcription of glutathione genes or activity of superoxide dismutase (SOD), catalase (CAT), and a decrease in the malondialdehyde (MDA). Immune responses showed significant increases in immunoglobulin M (IgM), lysozyme, and respiratory burst activity (RBA), and the expression of immune genes in several treatments. Notably, EA at 0.2 g and EP 2 elicited a stronger response than the other dosages for these parameters in Nile tilapia. These findings suggest that dietary supplementation with EA, PP, or their combination enhances growth performance, immune responses, and antioxidant capacity in O. niloticus , with the EA 0.2 g and EP 2 treatments showing the most pronounced effects.