Dietary DHA/EPA ratio affects growth, tissue fatty acid profiles and expression of genes involved in lipid metabolism in mud crab Scylla paramamosain supplied with appropriate n-3 LC-PUFA at two lipid levels

Abstract

An 8-week feeding trial was conducted to determine the optimal dietary docosahexaenoic acid/eisosapentaenoic acid (DHA/EPA) ratio of mud crab (Scylla paramamosain) supplied with optimal n-3 LC-PUFA at two dietary lipid levels. Eight isonitrogenous diets were formulated to contain 7% and 12% crude lipid, each with DHA/EPA ratios of 0.6, 1.2, 2.3 and 3.2, respectively. Each diet was randomly assigned to triplicate groups of 30 juvenile mud crabs (initial weight 20.9 ± 0.6g) that were stocked in single crab cells. In crabs fed 7% lipid, the diet with a DHA/EPA ratio of 2.3 showed significantly higher weight gain than crabs fed the other ratios while in crabs fed 12% lipid, lower weight gain and specific growth rate were observed in crabs fed the diet with a DHA/EPA ratio of 0.6 than crabs fed the other ratios. Lipid content in hepatopancreas significantly increased as dietary DHA/EPA ratio increased from 1.2 to 2.3 in crabs fed 7% lipid, while no differences were observed among crabs fed the diets with DHA/EPA ratios higher than 0.6 when fed 12% lipid. Total fatty acid and DHA contents and DHA/EPA ratio showed increasing, and EPA decreasing, trends in muscle and hepatopancreas with increased dietary DHA/EPA ratio, at both dietary lipid levels. The hemolymph triacylglycerol and total cholesterol contents were higher in crabs fed dietary DHA/PA ratios of 1.2 and 2.3 than those fed ratios of 0.6 and 3.2 at 7% dietary lipid, and lowest low and high-density lipoprotein cholesterol contents were observed in crabs fed DHA/EPA dietary ratios of 0.6 and 3.2 at 7% and 12% lipid, respectively. The expression levels of fas, aco3 and fatp4 were significantly up-regulated, and cptⅠ, hsl and ldlr were down-regulated, with increased dietary DHA/EPA ratio in crabs fed 7% lipid. In crabs fed 12% lipid, the expression levels of g6pd, 6pgd, srebp-1, aco1 and fatp4 were down-regulated, and fabp-1 was up-regulated, with increased dietary DHA/EPA ratio. The expression levels of elovl4 and Δ6 fad initially increased and then decreased as dietary DHA/EPA ratio increased from 0.6 to 3.2 in crabs fed both 7% and 12% lipid. Based on analysis of weight gain versus dietary DHA/EPA ratio, the optimal dietary DHA/EPA ratios of mud crab S. paramamosa were estimated to be 2.2 and 1.2 when supplied with optimal n-3 LC-PUFA at 7% and 12% lipid, respectively.