Growth, Antioxidant Defense, and Immune Response in <i>Labeo rohita</i> Fingerlings with the Dietary Vitamin C Supplementation

The study was designed to investigate the vitamin C supplementation effect on growth, oxidative stress, and immune response of Labeo rohita. Four diets 0, 200, 400, and 800 mg/kg was designed, 480 fingerlings with the initial weight 6.11 ± 0.08 g in triplicate groups were randomly distributed into 12 fiberglass tanks for 60 days. Growth results showed that final weight (13.87 ± 0.23–19.83 ± 0.34 g), weight gain (152.6 ± 2.7–251.1 ± 3.5%), and specific growth rate (1.91 ± 0.06–2.52 ± 0.03%/day) increased significantly (p < 0.05) with increasing dietary vitamin C levels, while feed conversion ratio (1.81 ± 0.04–1.29 ± 0.04) decreased (p = 0.006), indicating improved feed utilization. Survival rates were 91.1 ± 2.4% in the control, whereas they reached 98.4 ± 1.4% in the 800 mg/kg group. Antioxidant enzyme showed a significant (p < 0.01) enhancement. Superoxide dismutase (SOD) and catalase (CAT) activities increased from 25.6 ± 1.3 to 36.1 ± 1.3 U/mg protein and 12.4 ± 0.7 to 20.1 ± 0.5 U/mg protein. The malondialdehyde (MDA) levels reduced significantly (p = 0.005), while glutathione (GSH) concentration increased significantly (p = 0.007) from 3.10 ± 0.13 to 4.41 ± 0.13 µmol/g tissue. Immune response parameters were also positively affected by dietary vitamin C. Lysozyme activity increased significantly (p = 0.008) from 15.4 ± 0.3 to 23.4 ± 0.6 U/mL, respiratory burst activity improved from 0.178 ± 0.006 to 0.261 ± 0.006 OD₆₃₀ nm, and phagocytic activity rose from 28.3 ± 1.4 to 41.4 ± 1.4%. Similarly, nitric oxide production increased from 4.13 ± 0.28 to 6.86 ± 0.26 µmol/L. Total protein, albumin, and globulin were also significantly raised (p < 0.05). The study concluded that dietary vitamin C can be used to increase growth, support antioxidant defense, and improve immune responses in L. rohita