Effects of Norbixin on Growth Performance, Immunomodulation, Antioxidant Systems, and Metabolic Alterations in the Oriental River Prawn ( Macrobrachium nipponense ): An Integrative Analysis

BACKGROUND: Natural carotenoids have gained considerable attention in aquaculture due to their potential to enhance growth performance, physiological status, and product quality in crustaceans. However, limited information is available regarding the dietary effects of norbixin on Macrobrachium nipponense. OBJECTIVES: This study evaluated the effects of dietary norbixin supplementation on growth performance, haemato-biochemical indices, immune responses, antioxidant status, digestive enzyme activity, intestinal microbiota, carotenoid accumulation, and body composition in M. nipponense. METHODS: A 56-day feeding trial was conducted using juvenile prawns (initial weight: 1.48 ± 0.07 g) fed diets supplemented with 0.00, 0.05, 0.10, 0.15, and 0.20 g/kg norbixin. Growth indices, biochemical and immunological parameters, antioxidant capacity, digestive enzyme activities, intestinal bacterial populations, tissue carotenoid deposition, and proximate body composition were subsequently assessed. RESULTS: Dietary norbixin significantly improved growth performance, feed conversion ratio, hepatosomatic index, and survival rate, with the most pronounced effects observed at 0.15 g/kg (p < 0.05). Dissolved oxygen levels also increased dose-dependently and peaked in the 0.15 g/kg treatment (p < 0.05). Serum urea, uric acid, glucose, creatinine, cholesterol, and triglyceride concentrations decreased significantly, whereas high- and low-density lipoprotein levels increased (p < 0.05). Immune responses and total antioxidant capacity were enhanced, while glutathione peroxidase, alkaline phosphatase, and acid phosphatase activities remained unaffected (p > 0.05). Norbixin supplementation further enhanced digestive enzyme activities, increased lactic acid bacteria abundance, reduced total bacterial counts, and promoted carotenoid accumulation in muscle, shell, and hepatopancreas (p < 0.05). Whole-body crude protein and lipid contents increased, whereas moisture and ash contents decreased (p < 0.05). CONCLUSIONS: Dietary supplementation with 0.15 g/kg norbixin effectively enhanced growth, immunocompetence, antioxidant defence, intestinal microbial balance, carotenoid deposition, and nutritional quality in M. nipponense, suggesting its potential as a functional feed additive in freshwater prawn aquaculture.