Dietary chromium picolinate-promoted oxidative phosphorylation may be a potential mean to improve hypoxia tolerance of juvenile grass carp ().

This study aimed to investigate the effects of dietary chromium picolinate (Cr-Pic) on growth performance, glucose (GLU) metabolism, and hypoxia tolerance of juvenile grass carp (). A total of 2160 juvenile grass carp (10.98 ± 0.01 g) were randomly divided into six groups with six cages each, containing 60 fish per cage. They were fed experimental diets with chromium (Cr) at 0.00 (basal diet), 0.40, 0.80, 1.20, 1.60, and 2.00 mg/kg (actual contents: 0.25, 0.67, 1.08, 1.63, 2.08, and 2.65 mg/kg, respectively) for 10 weeks. Then, 96 fish were selected and divided into a normoxia group ( = 48) and a hypoxia group ( = 48) for a 96 h hypoxia trial. The growth trial results showed that, compared to the 0.25 mg/kg Cr group, the 0.67 to 2.65 mg/kg Cr groups enhanced the percent weight gain (PWG; < 0.001) and increased the protein retention value ( < 0.001), and promoted the growth and development of juvenile grass carp. In the hypoxia group, dietary 1.08 mg/kg Cr reduced the activities of serum glutamic pyruvic transaminase (GPT; < 0.001) and glutamic oxaloacetic transaminase (GOT; < 0.001), thereby alleviating liver damage. Furthermore, dietary 1.63 mg/kg Cr also increased glycolysis, the tricarboxylic acid cycle, and oxidative phosphorylation in juvenile grass carp under hypoxia stress, as evidenced by the enhanced activities of liver enzymes, such as hexose kinase ( 0.001), pyruvate kinase ( 0.001), and malate dehydrogenase ( 0.001). Additionally, in the liver, dietary 1.08 to 1.63 mg/kg Cr inhibited the expression of proteins related to gluconeogenesis, like glucose-6-phosphatase ( 0.001) and phosphoenolpyruvate carboxykinase ( 0.001), and elevated the relative mRNA expression levels of mitochondrially encoded NADH dehydrogenase I ( 0.001) and adenosine triphosphate (ATP) synthase-coupling factor 6 ( 0.001), thereby increased ATP production under hypoxia stress. Moreover, in the hypoxia group, dietary 1.08 to 1.63 mg/kg Cr up-regulated the liver relative mRNA expression levels of nuclear respiratory factor 1 ( 0.001) and mitofusin 1 ( 0.001), and down-regulated the relative mRNA expression levels of mitochondrial fission protein 1 ( 0.001) and B-cell lymphoma-2-interacting protein 3 ( 0.001), which contributed to the maintenance of normal mitochondrial function. Regression analysis was conducted utilizing the parameters of PWG, GPT activity, and ATP content, and the dietary Cr requirements of juvenile grass carp were 1.02, 1.55, and 1.54 mg/kg, respectively. Overall, this study provided new insights into the effects of Cr on GLU metabolism of juvenile grass carp under hypoxia stress, offering a nutritional regulation strategy for improving the ability of fish to resist hypoxia stress.