Effects of dietary carbohydrate and protein levels on the growth performance, nutrient metabolism and flesh quality of channel catfish (Ictarulus punctatus)

This study aimed to evaluate the effects of dietary carbohydrate and protein levels on growth performance, nutrient metabolism, liver function and flesh quality of channel catfish ( Ictarulus punctatus ). Four experimental diets were designed containing 20 % or 32 % carbohydrate with 32 % or 36 % protein, respectively (C20P32, C20P36, C32P32 and C32P36) and fed to triplicated groups of channel catfish (initial body weight: 60.88 ± 0.42 g) for 8 weeks. A two-way ANOVA revealed significant interactions between dietary carbohydrate and protein levels, influencing growth performance, VSI, LRE, body composition (lipid, moisture and ash), plasma metabolites (T-CHO, TG, HDL-C and LDL-C), liver T-CHO level and g6pase mRNA expression. Higher dietary carbohydrate increased FE, IPF, CF and PER, whereas higher protein level reduced PRE and PER. High carbohydrate intake promoted hepatic glucose transport ( glut2 ), glycolysis ( gk , pfkl , pkl ), glycogenesis ( gys2 ), glycogenolysis ( pygl ) and lipogenesis (TG content, Oil Red O area, expression of acaca , srebp1 , fasn and scd ). Concurrently, it suppressed lipolysis ( lpl , perilipin , cpt-1a , aco and pparα ), resulting in increased glycogen and lipid accumulation in the liver. Moreover, high carbohydrate decreased AST activities and up-regulated the expression of protein synthesis genes ( mtor , s6k1 and s6 ) in liver. Notably, there were no significant differences in plasma ALT, AST and AKP levels, liver ROS and MDA contents as well as the expressions levels of liver inflammatory cytokines ( tgfβ , tnfα , il6 and il1β ) among the groups. In terms of white muscle, dietary carbohydrate and protein levels interacted to affect lipid content, the expression levels of genes involved in lipid and glycogen metabolism, mrf4 expression level, fatty acid profiles (EPA, DHA, n-3 PUFA and PUFA) and texture properties (flexibility, adhesiveness and stringiness). Furthermore, high carbohydrate increased muscle glycogen, lactate and LDH contents, while decreased water holding capacity and myf5 expression level in muscle. Higher protein level enhanced the ratio of n-3/n-6 PUFA, myog expression level and fracturability, but reduced toughness in muscle. In conclusion, the addition of carbohydrates to the diet of channel catfish had a protein-sparing effect. Dietary carbohydrate and protein levels didn’t affect liver function, while induced several modifications on flesh quality in channel catfish. • The addition of carbohydrates to the diet of channel catfish had a protein-sparing effect. • High carbohydrate increased glucose oxidation for energy supply and increased glycogen and lipid accumulation in liver. • High carbohydrate promoted protein deposition which is linked to the activation of mTOR protein synthesis pathway. • Dietary carbohydrate and protein levels induced several modifications on flesh quality.