The effects of high‐macronutrient (protein, fat and carbohydrate) diets on growth performance and muscular metabolic responses in grass carp

Four purified diets were fed to quadruplicate groups of grass carp (Ctenopharyngodon idella) (initial body weight 55 g; 20 fish per replicate) for 11 weeks. The gross energy of three high-macronutrient diets was 11% higher than that of the control diet. The high-protein diet led to the highest weight gain (WG) and specific growth rate (SGR), while the lowest protein efficiency ratio (PER) and protein retention efficiency (PRE) (p < .05). No significant effect on the above four indexes was observed in fish fed the high-fat diet (p > .05). Fish fed high-carbohydrate diet had the lowest WG and SGR (p < .05), while no significant difference was found in PER and PRE (p > .05). The contents of crude fat, total polyunsaturated fatty acids in muscle in high-fat and high-carbohydrate groups, but not in high-protein group, were significantly higher than those of control group (p < .05). The contents of muscular protein and most amino acids did not show any clear change in response to high-macronutrient diet (p > .05). Gene expression data in muscle indicated that g6pd, fas and acc1 in muscle were up-regulated in high-fat and high-carbohydrate groups, and fbp and pck were significantly up-regulated in high-macronutrient groups (p < .05). In conclusion, the high-fat and high-carbohydrate diets increased muscular fat deposition by up-regulation the key enzymes expressions of pentose phosphate pathway and fat synthesis, and high-macronutrient diets increased muscular glycogen content by up-regulation gluconeogenesis enzymes expressions.