Two Strains of Gibel Carp (Carassius gibelio) Exhibit Diverse Responses to Carbohydrates in a Low-Lipid Diet

Abstract

An 8-week feeding trial was conducted to investigate carbohydrate use in a low-lipid diet between different strains of gibel carp (Carassius gibelio). The wild-type Dongting strain and artificially selected CASIII strain were fed three levels of carbohydrate: 15%, 30%, and 45%, in a low-lipid formulation (4%). The results showed that low-lipid supplementation with high carbohydrate seems to improve the feeding rate (FR) and specific growth rate (SGR), while it did not result in hyperglycaemia in gibel carp. Transcriptional regulation was slightly affected by carbohydrate levels; only hepatic pfk expression was more increased in the 30% and 45% carbohydrate diets than in the 15% carbohydrate diet ( $p<0.05$ ). Regarding the strains, CASIII obtained higher growth performance by having higher FR and SGR than Dongting ( $p<0.05$ ). Relatively higher glycaemia was found in CASIII, and it was coupled with increased plasma triglycerides and insulin ( $p>0.05$ ). Enhanced gene expression of pk involved in glycolysis and decreased mRNA levels of pepck in gluconeogenesis were also observed in CASIII ( $p<0.05$ ). There were strong $\text{strain}\ast \text{diet}$ interactions of gene expression involved in lipogenesis, and Dongting had higher mRNA levels of srebp-1, acly, and fas when fed carbohydrate at 45% ( $p<0.05$ ). In conclusion, the tolerant level of carbohydrates in a low-lipid diet could be up to 45% for gibel carp by an improvement of growth and noninducement of postprandial plasma glucose. CASIII had a better ability to use dietary carbohydrates for growth with active glycolysis and restrained gluconeogenesis, and Dongting had more potential in lipid metabolism in response to carbohydrate intake.