Effects of Dietary Carbohydrate Levels on Growth Performance, Antioxidant Capacity, and Hepatointestinal Health in Schizopygopsis younghusbandi

Schizopygopsis younghusbandi is an endemic and ecologically important fish species on the Tibetan Plateau. However, its dietary carbohydrate requirement remains unexplored, limiting the development of cost-effective and physiological-friendly artificial feed. This study investigated the effects of different dietary carbohydrate levels on the growth performance, antioxidant capacity, and hepatointestinal morphology of S.younghusbandi. Six experimental diets were formulated with graded carbohydrate levels of 9% (C9), 12% (C12), 15% (C15), 18% (C18), 21% (C21), and 24% (C24). A total of 720 fish (initial weight 37.49 ± 0.25 g) were randomly allocated to six groups in quadruplicate (30 fish per replicate) and reared in tanks (0.6 m × 0.5 m × 0.4 m) for 8 weeks. Results demonstrated that the diet in the C12 group significantly improved weight gain rate (WGR), specific growth rate (SGR), and feed conversion ratio (FCR) (p < 0.05). Regression fitting analysis on growth performance indicated that the optimal carbohydrate level ranged from 10.42% to 10.49%. Additionally, the C12 group exhibited enhanced total superoxide dismutase (T-SOD) activities and reduced malondialdehyde (MDA) content in the liver, along with reduced interleukin-1β (IL-1β) levels in the serum (p < 0.05). Histological analysis revealed superior hepatointestinal integrity in the C12 group, characterized by lower hepatic lipid droplet accumulation, reduced vacuolation, decreased hepatosomatic index (HSI) (p < 0.05), as well as higher intestinal villus height and muscle thickness (p < 0.05). In conclusion, the C12 group optimally enhanced the growth, antioxidant response, and hepatointestinal health of S. younghusbandi, indicating that the suitable dietary carbohydrate level for this species is 12%.