Effects of dietary histidine levels on growth performance, body composition and intestinal enzymes activities of juvenile Jian carp (Cyprinus carpio var. Jian)

A total of 1200 juvenile Jian carp (Cyprinus carpio var. Jian) (8.76 +/- 0.02 g) were fed diets containing graded levels of histidine at 2.3 (unsupplemented control), 4.4, 6.3, 8.6, 10.8 and 12.7 g kg-1 diet for 60 days to investigate the effects of histidine levels on growth performance, body composition, intestinal enzymes activities and microflora. Specific growth rate (SGR), feed efficiency, protein efficiency ratio, protein productive value, body protein content and lipid content of fish were lowest in fish fed the basal diet (P < 0.05). Activities of glutamate-pyruvate transaminase in muscle and hepatopancreas, trypsin, chymotrypsin, amylase, lipase activities in intestine and hepatopancreas, and Na+, K+-ATPase, creatine kinase, alkaline phosphatase, gamma-glutamyl transpeptidase activities in three intestinal segments were improved by dietary histidine (P < 0.05), whereas glutamate-oxaloacetate transaminase activities and plasma ammonia content followed an opposite trend. The amounts of Lactobacillus, Escherichia coli and Aeromonas were significantly affected by dietary histidine levels (P < 0.05). These results suggested that histidine could improve growth and enhance intestinal enzymes activities of juvenile Jian carp. The dietary histidine requirement of juvenile Jian carp (8.7668.02 g) based on SGR was 7.8 g kg-1 diet or 2.38 g 100 g-1 protein by quadratic regression analysis.