Effects of dietary carbohydrate-to-lipid ratios on growth performance, intestinal digestion, lipid and carbohydrate metabolism of red swamp crayfish (Procambarus clarkii)

Understanding the effects of dietary nutrients on physiological and biochemical parameters, especially the metabolism of nutrients during crayfish farming, can be useful for improving crayfish health and optimizing production in aquaculture. Therefore, we conducted an 8-week feeding study to investigate the effect of dietary carbohydrate-to-lipid (CHO: LIP) ratios on growth performance, hemolymph biochemical indices, intestinal digestion, hepatopancreas lipid, and carbohydrate metabolism of red swamp crayfish (Procambarus clarkii) (initial weight = 9.10 +/- 0.15 g). Four isoenergetic and isonitrogenous diets (16.2 MJ kg(-1) gross energy and 30.2% crude protein) were estimated to include different CHO:LIP ratios: 1.88 (22.5% CHO/11.9% LIP); 3.25 (29.3% CHO/9% LIP); 5.94 (36.2% CHO/6.1% LIP); and 13.60 (43.1% CHO/3.2% LIP). According to the results, the weight gain rate (WGR), final body weight, specific growth rate (SGR), intestinal amylase activity, abdominal muscle crude protein content, and protease activity significantly increased (P < 0.05) as the CHO:LIP ratio increased from 1.88 to 5.94 and then significantly decreased (P < 0.05) as the CHO:LIP ratio increased from 5.94 to 13.60. However, the feed conversion ratio exhibited the opposite trend. The abdominal muscle crude lipid content, hemolymph cholesterol content, and intestinal lipase activity significantly decreased with increasing dietary CHO:LIP ratios from 1.88 to 13.60, whereas the hemolymph glucose level showed the opposite trend. The activities of phosphofructokinase (PFK), the mRNA expression levels of pfk, pyruvate kinase (pk), lactate dehydrogenase (ldh), fatty acid synthase (fas), cholesterol regulatory element-binding protein 1 (srebp1), retinoic acid X receptor (rxr), and hexokinase (hk) in the hepatopancreas significantly increased with the increasing CHO: LIP ratios from 1.88 to 13.60, whereas the activities of lipoprotein lipase, hepatic esterase, and phosphoenolpyruvate carboxykinase, the mRNA expression levels of acyl coenzyme a oxidase (aco), fatty acid-binding protein gene (fabp), acyl-coA synthetase bubblegum (acsbg), glucose6-phosphatase (g6pase), pepck and fructose-1, 6-diphosphatase (fbpase) significantly decreased. The quadratic regression model showed that the optimal CHO: LIP ratio and dietary protein level for red swamp crayfish were 7.74% and 30%, respectively. These results suggest that optimal dietary CHO: LIP ratios could increase the SGR and WGR of red swamp crayfish. High CHO: LIP ratio inhibits gluconeogenesis and lipid degradation, while low CHO: LIP ratio inhibits glycolysis and lipogenesis.