Effects Of Dietary Tryptophan On The Growth Performance,Immunity And Intestinal Health Of Northern Snakehead（Channa Argus Cantor,1842）

A 70-day feeding trial was undertaken to indicate the effects of dietary L-tryptophan levels on growth performance,immunity,antioxidant capacity and intestinal health of northern snakehead（Channa argus Cantor,1842）.540 juvenile fish（10.21±0.11 g）were randomly distributed into 18 net cages with six treatments and three replicates.The fish were fed with six isonitrogenous（48.56%protein）and isoenergetic（19.72 KJ of gross energy g-1）experimental diets supplemented with different levels of L-tryptophan（0.19%,0.30%,0.39%,0.48%,0.59%and 0.68%）.The fish were hand-fed twice a day at apparent satiation level.The completed experiments were presented briefly as follows:1.The experiment was determined to investigate the dietary tryptophan levels on growth performance and feed utilization,proximate composition and amino acid content of dorsal muscle,activities of the digestive enzymes in intestine and activities of the amino acid metabolic enzymes in liver of Cargus.The results showed that the final weight,weight gain,specific growth rate,feed efficiency,protein efficiency ratio,the crude protein content in dorsal muscle,glutamate dehydrogenase activity and glutamate oxaloacetate transaminase activity in liver were markedly upgraded,with the dietary tryptophan increasing to 0.48%（P<0.05）.The content of Methionine,Histidine,Threonine,Glycine,Phenylalanine and Glutamic acid in dorsal muscle of fish was also significantly affected by the dietary tryptophan levels（P<0.05）.Meanwhile,the highest pepsin activity was found in fish fed with 0.39%dietary tryptophan（P<0.05）.0.30%to 0.48%dietary tryptophan levels significantly improved the lipase activity in intestine of fish（P<0.05）.However,the glutamate pyruvate transaminase activity in liver was significantly improved with the dietary tryptophan level increased（P<0.05）.Based on the second-degree polynomial regression analysis of specific growth rate and feed efficiency against the dietary tryptophan levels,the optimum dietary tryptophan requirement for C.argus was respectively estimated to be 0.46%and 0.45%of the diet,corresponding to 0.95%and 0.93%of dietary protein.2.The feeding trial was carried out to observe the dietary tryptophan levels on body index,total hemocyte counts,hematologic antioxidant parameters and blood immune enzyme activity of C.argus.The results indicated that hepatosomatic index,spleen index and renal index of fish fed with 0.39%and 0.48%dietary tryptophan were significantly higher than that with 0.68%dietary tryptophan（P<0.05）.The highest total hemocyte counts was found in fish fed with 0.39%and 0.48%dietary tryptophan（P<0.05）.In terms of hematologic antioxidant parameters,fish fed with 0.39%and 0.48%dietary tryptophan had the highest total antioxidant capacity activity and the lowest malondinaldehyde value（P<0.05）.The highest catalase activity was found in fish fed with 0.30%dietary tryptophan,the lowest was found in fish fed with 0.68%dietary tryptophan（P<0.05）.Additionally,fish fed with 0.48%dietary tryptophan had the highest superoxide dismutase activity（P<0.05）.Meanwhile,fish fed with 0.39%dietary tryptophan had the highest acid phosphatase and alkaline phosphatase activities（P<0.05）.These results suggested that appropriate tryptophan could improve the organ index,total hemocyte count,antioxidant capacity and immunity of C.argus.3.In order to investigate the effects of dietary tryptophan levels on intestinal health of Cargus,the relative mRNA expression of genes related to the target of rapamycin signaling pathway,the intestinal inflammatory factors and the intestinal physiological barrier were determined.The results showed that 0.48%dietary tryptophan significantly upregulated the myeloid differentiation primary response 88 mRNA levels（P<0.05）.The highest mRNA levels of toll Like receptor-2,toll Like receptor-4 and toll Like receptor-5 were found in fish fed with 0.39%dietary tryptophan,while the highest phosphoinositide-3-kinase catalytic alpha gene mRNA levels was found in fish fed with 0.68%dietary tryptophan（P<0.05）.Fish fed with 0.30%and 0.39%dietary tryptophan had the highest interleukin 8 and interleukin 22 mRNA levels（P<0.05）.Furthermore,0.39%dietary tryptophan level significantly improved claudin and occludin mRNA levels（P<0.05）.Overall,the results suggested that dietary tryptophan could regulate the intestinal health of C.argus via activating the target of rapamycin signaling pathway,appropriate dietary tryptophan seemed to be more beneficial to promote the intestinal health of C.argus.