Peel of pumpkin (Cucurbita pepo) diets boost growth, digestive-absorptive functions, immune-antioxidant indices, and regulate immunomodulatory genes and mTOR/MAPK-P38/apoptosis signaling pathway in Oreochromis niloticus

Abstract

Much attention has been focused on the potential application of industrial by-products as feed supplements in fish diets. The current study examines the effects of feeding pumpkin (Cucurbita pepo) peel powder (CPP) on growth, digestive processes, immune-antioxidant parameters, and gene expression that regulates these processes in Nile tilapia (Oreochromis niloticus). Additionally, fish resistance to Aeromonas veronii was assessed. Fish (n = 200; 34.93 ± 0.11 g) were split equally into four groups and kept for 60 days. Fish were given diets supplemented with different CPP levels: 0 (CPP0 was the control diet), 5 (CPP5), 10 (CPP10), and 15 (CPP15) g CPP/kg diet. The findings showed that CPP meals significantly increased (P˂0.05) growth, intestinal morphometrics, and digestive enzyme activity. The optimum dietary level of CPP was 12 g/kg diet according to the broken line regression analysis based on the data of weight gain and feed conversion ratio. CPP diets up-regulated (P˂0.05) the intestinal and muscular gene expression (trypsin, solute carrier family 6, member 18, fatty acid-binding proteins-2, cluster of differentiation 36, insulin growth factor-1, carnitine palmitoyl-transferase-1alpha, pyruvate kinase, and glucokinase). CPP diets improved the immune-antioxidant indices (P˂0.001) (lysozyme, complement 3, myeloperoxidase, superoxide dismutase, reduced glutathione content, and total antioxidant capacity). Moreover, CPP diets increased (P˂0.05) the splenic expression of heme oxygenase-1, interleukins (IL-6 and IL8), tumor necrosis factor-alpha, and nuclear factor erythroid-related factor 2. CPP diets caused down-regulation (P˂0.05) of the splenic expression of the tumor suppressor gene (P53), mitogen-activated protein kinase (P38), caspase-9, and mechanistic target of rapamycin. During the A. veronii challenge, the fish survival percentage increased with CPP diets. Noteworthy, CPP diets could improve Nile tilapia immunity, growth, and disease resistance. Moreover, the best dietary level of CPP was 12 g/kg diet for sustainable Nile tilapia aquaculture.