Effects of graded levels of histidine on growth performance, digested enzymes activities, erythrocyte osmotic fragility and hypoxia-tolerance of juvenile grass carp Ctenopharyngodon idella

A 10-week experiment was conducted to estimate the effects of graded levels of histidine on growth performance, digested enzymes activities, erythrocyte osmotic fragility and hypoxia-tolerance of juvenile grass carp Ctenopharyngodon idella. Six isonitrogenous (38%) and isoenergetic semi-purified diets containing casein and gelatin with graded levels of histidine (0.45, 0.72, 1.02, 1.28, 1.55, 1.78 g 100 g(-1) DM) were formulated. Each diet was assigned to triplicate groups of 30 fish (3.68 +/- 0.01) for each tank. The highest weight gain (WG, %), final body weight (FBW, g) and specific growth rate (SGR) were recorded when histidine level was 1.02% of the diet. Whole body protein andmuscle protein were not significantly affected by the histidine level (P > 0.05). Muscle histidine content was linearly increased along with the dietary histidine increasing (P < 0.05). Fish fed histidine deficient diet (0.45 g 100 g(-1)) exhibited highest erythrocyte osmotic fragility (P < 0.05). Meanwhile, the shortest survival time and lowest catalase (CAT) activity and total antioxidant capacity were also recorded in fish fed histidine deficient diet (P < 0.05). Second-degree polynomial regression analysis of final body weight data indicated that the minimum recommended dietary histidine requirement for grass carp was 1.21% of the diet, corresponding to 3.2% of dietary protein. Statement of relevance: The present study determined optimum dietary histidine requirement for juvenile grass carp and the data goes to 1.21% of the diet, corresponding to 3.2% of dietary protein. We also found that juvenile grass carp fed with histidine deficiency diet not only limited their growth performance, but also exhibited higher erythrocyte osmotic fragility, lower hypoxia-tolerance and antioxidant enzyme activities. Digested enzyme activities were also significantly affected by the dietary histidine levels. Thus, it is important to meet histidine requirement when commercial diets are formulated for this species. (C) 2015 Elsevier B.V. All rights reserved.