Effect of dietary choline on growth, intestinal enzyme activities and relative expressions of target of rapamycin and eIF4E-binding protein2 gene in muscle, hepatopancreas and intestine of juvenile Jian carp (Cyprinus carpio var. Jian)

The effects of dietary choline on growth, digestive and absorptive capacities, and target of rapamycin (TOR) and eIF4E-binding protein2 (4E-BP2) gene expression in muscle, hepatopancreas and intestine of juvenile Jian carp (Cyprinus carpio var. Jian) were assessed. A total of 1200 juvenile Jian carp with an average initial weight of 7.94±0.03g were fed six semi-purified diets containing 165 (unsupplemented control group), 310, 607, 896, 1167 and 1820mgcholinekg⁻¹ diet for 65days. Specific growth rate (SGR), feed intake, feed efficiency, protein retention value, protein content and lipid content of fish carcasses were significantly improved by dietary choline supplementation; whereas, protein efficiency ratio and body ash content were not significantly different among dietary groups. Patterns of differences in intestine length, relative gut length, intestine weight, hepatopancreas protein content, intestinal folds height in three intestinal segments, trypsin and chymotrypsin activities in intestine and hepatopancreas, α-amylase and creatine kinase activities in intestine, Na⁺/K⁺-ATPase activity in distal intestine and relative expression of TOR gene in distal intestine and 4E-BP2 gene in muscle responded similar to SGR; whereas, the trends of hepatosomatic index, lipase activity in intestine and hepatopancreas, Na⁺/K⁺-ATPase activity in proximal intestine and mid intestine, TOR gene expression in muscle and hepatopancreas, and 4E-BP2 gene expression in proximal intestine, mid intestine and distal intestine were opposite. Alkaline phosphatase and γ-glutamyl transpeptidase activities in intestinal segments were not significantly different among dietary groups. These results indicated that dietary choline could improve fish growth, enhance digestive and absorptive ability and regulate TOR and 4E-BP2 gene expression in tissues. The dietary choline requirement of Jian carp estimated by the broken-line model based on SGR was 566mgcholinekg⁻¹ diet in the form of choline chloride.