Adaptations of lipid metabolism and food intake in response to low and high fat diets in juvenile grass carp (Ctenopharyngodon idellus)

• Fish induce glycolysis (gk, pk), increase lipogenesis (acc, fas) and depress lipolysis (cpt1) to adapt to low lipid intake.
• Fish reduce lipogenesis (acc), induce β-oxidative (pparα) and increase gluconeogenesis (g6pase) to adapt to high lipid intake.
• Increased FA or glucose might induce the appetite suppression by high dietary lipid through modulation of leptin expression.

This study was conducted to examine the systemic metabolic strategies of grass carp to maintain lipid homeostasis when fed with low- or high-fat diets. The isonitrogenous diets with different fat levels (9.3, 48.7 and 107.9 g kg− 1) were fed to grass carp for 8 weeks. After the feeding trial, the growth rate and feed intake of grass carp fed with low-lipid (LL) diet or high-lipid (HL) diet were lower than fish fed with medium-lipid (ML) diet. Serum triglyceride (TG) and total body fat contents were significantly increased in grass carp with increasing lipid intake. Gene expression data indicated that fish increased hepatic gk and pk expressions to elevate glycolysis, and enhanced acc and fas expressions to accelerate biosynthesis of fatty acid (FA) to adapt to low lipid intake. Meanwhile, fish fed with LL diet decreased hepatic cpt1 expression to depress lipolysis, leading to low contents of serum TG and body fat. In contrast, excess lipid intake increased g6pase, pepck and pparα expressions to stimulate gluconeogenesis and β-oxidative, while decreased acc and fas expressions to reduce lipid synthesis in fish liver. Moreover, increased β-oxidative-induced FA or gluconeogenesis-induced serum glucose might induce the appetite suppression by high dietary fat through modulation of leptin expression. This study could be a reference in the systemic adaptation of lipid metabolism responding to dietary fat in fish.Statement of relevanceSystemic adaptation of lipid metabolism responding to dietary lipid.