Dietary Arginine Regulates Glycometabolism in Hybrid Grouper ( <i>Epinephelus fuscoguttatus</i> ♀ × <i>Epinephelus lanceolatus</i> ♂) via the IGF‐1 and NO‐cGMP Pathways

The hybrid grouper ( Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂), a typical carnivorous fish, has a limited ability to utilize dietary carbohydrates (CHOs). This study investigated the effects of different dietary arginine (Arg) levels (2.55 and 3.65%) and CHO‐to‐lipid ratios (C/L: 3.57, 2.39, 1.61) on the glycometabolism of hybrid grouper. Juvenile hybrid grouper (mean initial body length and weight: 7.8 cm and 13.04 g) were manually fed to fullness two times per day throughout a 7‐week growth trial. The results showed that the C/L3.67 diets significantly elevated 2‐h postprandial blood glucose concentration, as well as reduced hepatic glycogen level, intraperitoneal fat ratio (IPF), and the whole‐body and hepatic lipid contents relative to the C/L2.39 and C/L1.61 diets. Dietary Arg supplementation significantly improved this metabolic disorder. These improvements were associated with enhanced plasma insulin‐like growth factor 1 (IGF‐1) concentration, hepatic phosphofructokinase (PFK) activity, nitric oxide (NO), and cyclic guanosine monophosphate (cGMP) levels. They were also linked to the upregulated expression of key molecules in related pathways, including IGF‐1 receptor (igf1r), phosphatidylinositol 3‐kinase (pi3k), protein kinase AMP‐activated catalytic subunit α (ampk‐α), and protein kinase B (Akt) genes, as well as glucose transporter 4 (GLUT4) and mechanistic target of rapamycin (mTOR) proteins. Generally, suitable dietary Arg supplementation can reduce postprandial blood glucose and hepatic glycogen concentrations in hybrid grouper fed high C/L diets by regulating key genes and proteins within the IGF‐1 and NO‐cGMP pathways. This finding provided a nutritional intervention to enhance CHO utilization in hybrid grouper aquaculture.