Dietary vitamin C modulates antioxidant capacity, immune responses and muscle hydroxyproline concentration in juvenile Pacific white shrimp (Penaeus vannamei).

Vitamin C (VC) plays a crucial role in regulating redox homeostasis; however, its biochemical responses in Penaeus vannamei to graded dietary levels, particularly in relation to immune, antioxidant defense and structural protein metabolism remain insufficiently characterized. This study therefore investigated the physiological and biochemical modulations and VC requirement of P. vannamei by evaluating the effects of graded vitamin C concentrations (5.99-157.78 mg/kg) on growth, immune responses, hepatopancreas vitamin C concentration and muscle hydroxyproline and collagen concentrations. Six diets were formulated to contain VC at levels of 0, 30, 60, 90, 120 and 150 mg/kg (designated as C0, C30, C60, C90, C120 and C150, respectively). Quadruplicate groups of 20 shrimp (0.70 ± 0.01 g) were fed the diets for 49 days. Growth was significantly increased in shrimp fed C60, C90, C120 and C150 diets compared to the C0 group. Superoxide dismutase activity was significantly increased in C60, C90 and C120 groups in hemolymph, and significantly increased in C60, C90, C120 and C150 groups in hepatopancreas compared to the C0 group. Catalase activity and total antioxidant capacity were significantly increased in shrimp fed C90 diet compared to the C0 group. Hepatopancreas VC and muscle hydroxyproline and collagen concentrations were gradually increased with the increment in dietary VC concentrations (up to 63.1 mg/kg). Based on broken-line regression and second-order polynomial regression models in relation to growth and muscle hydroxyproline, the estimated optimum and maximum VC requirements varied from 77.8 to 151.7 mg/kg. These findings demonstrate that VC is a physiological modulator of redox balance and hydroxyproline synthesis of shrimp.