Caffeic acid phenethyl ester improves high-carbohydrate diet utilization by promoting adipocyte hyperplasia in grass carp (Ctenopharyngodon idellus).

Enhancing the ability of fish to consume a high-carbohydrate diet (HCD) is a key focus of aquaculture research. The propolis extract, caffeic acid phenethyl ester (CAPE) has anti-inflammatory, hepatoprotective, and glycolytic-promoting properties, but its potential to mitigate metabolic disorders in fish fed a HCD remains uncertain. This study investigated the effects of CAPE on the adaptability and utilization of a HCD in the herbivorous grass carp (Ctenopharyngodon idellus), focusing on growth performance, tissue and organ health, and nutrient metabolism. A total of 270 grass carp with an initial body weight of 12.69 ± 0.05 g were divided into five groups (Control, HCD, HCD + C200 [200 mg/kg CAPE], HCD + C500 [500 mg/kg CAPE], and HCD + C800 [800 mg/kg CAPE], respectively) with three replicates per group and fed for 8 weeks. Compared with Control group, the HCD reduced the final body weight, weight gain rate, specific growth rate, protein deposition rate, and crude protein in whole body and muscle (P < 0.05), and increased the feed conversion ratio, intraperitoneal fat index, and hepatosomatic index of grass carp (P < 0.05), whereas the addition of CAPE reduced these adverse effects (P < 0.05). Peroxisome proliferator-activated receptor γ (PPARγ) was activated by CAPE in adipose tissue (P < 0.05), but not in the hepatopancreas or muscle. These changes resulted in adipocyte hyperplasia (a smaller and more uniform distribution of adipocytes) and decreased immune cell penetration and inflammation. CAPE promoted the lipolysis and fatty acid β-oxidation in the adipose tissue, hepatopancreas, and muscle. CAPE improved glucose uptake and utilization-related gene expression in the hepatopancreas and muscle, alleviated hepatic steatosis, and promoted mammalian target of rapamycin (mtor) gene expression in muscle for grass carp on the HCD (P = 0.034). The addition of CAPE to the HCD inhibited inflammatory response in the adipose tissue, hepatopancreas, and muscle, and reduced the levels of alanine aminotransferase, aspartate aminotransferase, glucose, lactic dehydrogenase, low-density lipoprotein cholesterol, and triglycerides in the serum (P < 0.05). In summary, CAPE altered the pattern of adipose tissue expansion by promoting adipocyte hyperplasia, thereby promoting glucose and lipid metabolism, and ameliorated the adverse effects of a HCD on inflammation and growth performance in grass carp.