| This experiment was conducted to study the effects of dietary phenylalanine levels on growth performance, digestive and absorptive function, immune and antioxidant abilities of juvenile Jian carp(Cyprinus carpio var. Jian). A total of 1200 juvenile Jian carp (initial weight 7.53±0.01g) were fed diets with six levels of phenylalanine 1.9 (unsupplemented control),5.0,7.8,10.9,14.1 and 17.2 g kg-1 diet at a constant dietary tyrosine level of 15.4 g kg-1 diet. The feeding trial lasted for 60 days. Thirty fish were selected from each treatment to conduct a challenge trial with Aeromonas hydrophila after the feeding trial, and then feeding for 17 days.The results showed that phenylalanine deficiency results in caudal fan bending. Phenylalanine great significantly improved special growth ratio (SGR), feed intake (FI), feed efficiency (FE), protein efficiency ratio (PER), protein retention value (PRV) and lipid production value (LPV) (P＜O.01). Correlation analysis showed that SGR has significant positive correlation with FI and FE (r1=+0.988, r 2=+0.995, P< 0.01), and FE has significant positive correlation with PRV and LPV (r1=+0.995, r2=+0.995, P<0.0\). Phenylalanine great significantly increased activities of glutamate-oxaloacetate transaminase (GOT) and glutamate-pyruvate transaminase (GPT) in hepatopancreas, and GOT activity in muscle (P＜O.01), while the trends of GPT activity in muscle and plasma ammonia content were opposite. The data also showed that phenylalanine great significantly improved hepatopancreas weight, intestine length, intestine weight, folds height in proximal intestine (PI), mid intestine (MI) and distal intestine (DI), the activities of trypsin, amylase, lipase, chymotrypsin in hepatopancreas and intestine, creatinekinase activities in PI and DI, Na+, K+-ATPase,γ-glutamyl transpeptidase (γ-GT) and alkaline phosphatase (AKP) in PI, MI and DI (P＜0.01), while hepatopancreas and intestine protein content was not affected by dietary phenylalanine (P>0.05). The feed efficiency was positively correlated with creatinekinase activities in PI, AKP activities in MI,γ-glutamyl transpeptidase in DI, folds height in DI, hepatopancreas weight, intestine length, intestine weight and folds height in PI and DI (r1=+0.857, r2=+0.841, r3=+0.838, r4=+0.889, r5=+0.961, r6=+0.966, r7=+0.974, r8=+0.998, r9=+0.965, P＜0.05). Phenylalanine great significantly improved the counts of intestinal Lactobacillus and bacillus, and decreased the number of Escherichia coli and Aeromonas (P＜0.01). The dietary phenylalanine great significantly (P＜0.01) or significantly (P＜0.05) affected the GOT and GPT activities in serum, the activities of malondialdehyde (MDA), protein carbonyl (PC) and glutathione (GSH) content, superoxide dismutase (SOD), catalase (CAT), glutathione-S-transferase (GST) and glutathione reducase (GR) in serum, intestine, muscle, hepatopancreas, head kidney, hind kidney and spleen; phenylalanine also great significantly (P＜0.01) or significantly (P＜0.05) affected anti-superoxide anion (ASA) activities in serum, intestine, spleen and muscle, anti-hydroxy radical (AHR) activities in serum, intestine, hepatopancreas, muscle, spleen and head kidney, glutathione peroxidase (GPX) activities in serum, intestine, hepatopancreas, muscle, spleen and hind kidney, while anti-superoxide anion (ASA) activities in hepatopancreas, head kidney and hind kidney, anti-hydroxy radical (AHR) activity in hind kidney and glutathione peroxidase (GPX) activity in head kidney with no significantly difference with different phenylalanine levels (P> 0.05). Meanwhile, phenylalanine great significantly increased vaccinated survival rate, spleen weight, head kidney weight, hind kidney weight, phagocytosis of leucocyte, red and white blood cell count, addiment C3 and C4 content in serum, the activities of tartrateresistant acid phosphatase and lysozyme in serum, antibody titre to Aeromonas hydrophila and the content of IgM in serum (P＜0.01), nevertheless, great significantly decreased serum total iron binding capacity (P＜0.01).In conclusion, phenylalanine deficiency results in caudal fan bending. Phenylalanine promoted the growth of juvenile Jian carp and increased the feed efficiency, and the enhanced feed efficiency is correlated with the enhanced utilization of dietary protein and lipid; phenylalanine could elevate the jian carp's ability of digestive enzymes secretion, intestine absorption areas as well as absorptive ability by promoting the growth of hepatopancreas and intestine; phenylalanine could increase the counts of intestinal Lactobacillus and bacillus, decrease the counts of Escherichia coli and Aeromonas; phenylalanine promoted the growth of digestive organs'may be due to the developed ability of hepatopancreas and intestine anti-lipid peroxidation and anti-protein oxidative damage by phenylalanine supplement, and enzymatic antioxygen system as well as non-enzymatic antioxygen system changed correspondingly; meanwhile, phenylalanine could also decrease the lipid and protein oxidation of muscle, enhancing the body antioxidative ability of juvenile Jian carp; phenylalanine has the ability to promote the growth and antioxidative ability of immune organ such as head kidney and spleen, and non-specific immunity ability and specific immunity ability of Jian carp; The optimal dietary phenylalanine requirement for juvenile Jian carp (7.5-54.8 g) was 11.9 g kg-1 diet or 3.54 g (100 g)-1 protein in the presence of 15.4 g kg-1 diet dietary tyrosine based on quadratic regression against SGR. |
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