Dietary Arginine Regulates Glycometabolism in Hybrid Grouper (Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂) 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.