Effects of dietary pomegranate peel polyphenols on antioxidant capacity, immunity, lipid metabolism, and hepatointestinal health for golden pompano (Trachinotus ovatus)

The study investigated the effects of pomegranate peel polyphenols (PPPs) regarding growth performance, antioxidant capacity, lipid metabolism, immune function, and liver and intestine morphology in Trachinotus ovatus. The trial consisted of 6 groups, each receiving different concentrations of PPPs in their basal diet. The dosages used were 0, 10, 30, 90, 270, and 810 mg/kg, designated as P0, P1, P2, P3, P4, and P5, respectively. The feeding trial lasted for 56 days. In total, 270 fish, initially weighing 33.17 +/- 0.79 g, were selected and randomly allocated to 18 floating cages, with 15 fish in each cage. The outcomes demonstrated that the hepatosomatic index of the P3 and P4 groups reduced considerably than the control group (P0) (P < 0.05). The triglyceride (TG) in each experimental group decreased, while high-density lipoprotein (HDL-C) increased in the P4 and P5 groups, and low-density lipoprotein (LDL-C) decreased (P < 0.05).Furthermore, PPPs were found to enhance the antioxidant capacity of Trachinotus ovatus than the control group (P0), manifesting as an increase in serum superoxide dismutase (SOD) and total antioxidant capacity (T-AOC) levels and a decrease in malondialdehyde (MDA) content. Meanwhile, the mRNA expression levels of catalase (CAT), SOD, glutathione peroxidase (GSH-PX), HO-1, and Nrf-2 were increased, while the expression of Keap-1 was decreased. Regarding immunity, PPPs had a beneficial effect on the golden pompano. The levels of complement 3 (C3), complement 4 (C4), and lysozyme (LZM) in the serum were higher, while the IL-10 mRNA expression was enhanced, and the IL-8 and NF-kappa B expression levels were decreased compared to the P0 group. In relation to lipid metabolism, the addition of PPPs led to a reduction in the mRNA levels of the liver lipid metabolism gene Fas and an increase in the expression of CPT1, Apob-100, and PPAR alpha, as compared to the control group. Lastly, PPPs mitigated liver vacuolization and enhanced the height and width of intestinal villi in Trachinotus ovatus. In summary, the incorporation of PPPs effectively improved liver fat accumulation, antioxidant capacity, and non-specific immunity in Trachinotus ovatus. Based on the results of this study, we recommend that the addition amount of PPPs in the feed of Trachinotus ovatus is 270 mg/kg.