Spotted seabass, Lateolabrax maculatus can utilize the high-starch diet by effectively regulating the energy metabolism

Carbohydrates are the least cost feed source and conserve protein without affecting the growth of fish at a certain level. However, carnivorous fish fed with trophic levels >3.5 have a limited capability to utilize carbohydrates as an energy source. A 56-day feeding trial was conducted to evaluate the growth performance, hepatic histology, and glucose and lipid metabolism of spotted seabass, Lateolabrax maculatus (initial weight = 10.43 +/- 0.01 g), a typical carnivorous fish, fed low (130 g/kg) or high starch (202 g/kg) diets (named the LS or HS diets) under satiety and starvation conditions (3 h and 24 h postprandial). The results showed that compared with the LS diet, the HS diet did not negatively affect growth but slightly increased the FR and FCR of spotted seabass. A well regulated glucose metabolism response was observed in the HS group with significant downregulation of gluconeogenesis (G6P) and upregulation of glycolysis (PK) at 3 h postprandial (P3 h) and downregulation of glycolysis (GK, PFK-1) at the transcription level at 24 h postprandial (P24 h). However, hyperglycemic was still observed in the HS group with increased enzyme activities of gluconeogenesis (G6P) and glycolytic (PK) at P24 h, which indicated that the spotted seabass could not effectively regulate glycolytic under starvation conditions. Excessive starch intake significantly increased hepatic cAMP content, which enhanced the rate of basal metabolism to relieve hyperglycemia at P24 h. No hepatic glycogen accumulation was observed for both groups, and hepatic glycogen content was significantly decreased with upregulation glycogenolysis (PYGL) in the HS group under starvation conditions. In addition, and lipogenesis and lipolysis/beta-oxidation were not affected under satiety conditions (P3 h) in the HS group, while the mRNA levels of lipogenesis genes (FASN, ACC1) and beta-oxidation (CPT1 alpha, PPAR alpha) were downregulated under starvation conditions. These results indicated that spotted seabass could preferentially utilize glycogen and then lipids under starvation conditions. In conclusion, the spotted seabass could accelerate basal energy metabolism to relieve hyperglycemia and avoid glycogen accumulation and fatty liver after fed HS diet, and preferentially catabolized hepatic glycogen to provide energy under starvation conditions, which indicated that it could effectively regulate energy metabolism after feeding the HS diet.