Study On The Requirement Of Threonine And Arginine Of Triploid Oncorhynchus Mykiss Fed Low Fish Meal

The main research object of this paper is triploid O.mykiss,in order to study the effects of threonine and arginine levels on the growth,antioxidant capacity,digestive physiology,amino acid composition and intestinal anti-inflammatory factors of triploid O.mykiss fed with low fish meal.The main research contents and results of this paper are as follows:1.Study on dietary threonine requirement of triploid O.mykissIn this experiment,oncorhynchus mykiss were selected as the study subjects,a total of 5 experimental groups were set up,and 450 fish were randomly divided into 15 aquariums,and each experimental group had 3 replicates.Five isonitrogenous and lipid diets were prepared by adding L-threonine into the basal diet,and the levels were 0.45%(control),0.76%,1.09%,1.29% and 1.64%,respectively.By analyzing the experimental results,the final weight,specific growth rate and weight gain rate were significantly increased with the increase of threonine level(P<0.05)after the end of the experiment.Quadratic regression model was used to fit the content of threonine,PER and SGR in the feed.It was suggested that the optimal threonine level should be 1.2%～1.3%(2.89%～3.13% of the feed protein)to the triploid juvenile O.mykiss diet,and the crude fat content of the whole fish should be the lowest when the threonine level was 0.75%.There was significant difference between control group and control group(P<0.05).Water content was significantly decreased(P<0.05);The content of crude protein reached the peak when the THR level was 1.29%,and then decreased significantly with the increase of THR level.Threonine level had no significant difference in ash content among all groups(P>0.05).With the increase of threonine level,the serum malondialdehyde(MDA)content(P<0.05)was significantly decreased,while the activities of catalase(CAT)and superoxide dismutase(SOD)were still significantly enhanced,and reached the maximum value when the threonine level was 1.29%.The digestive enzyme activities of intestinal lipase(LPS)and trypsin were significantly higher than those of the control group(P<0.05),but decreased with the THR level reaching 1.64%.THR level significantly affected the expression levels of intestinal inflammatory factors IL-2,IL-8,IL-10,Ig M,TNF-α and Pep T1 genes(P<0.05).With the increase of THR level,IL-2,Ig M and Pep T1 were firstly increased and then decreased.The highest expression level was found in 1.29% and 1.09% groups.Il-8increased gradually.Il-10 and TNF-α showed a decreasing trend.To sum up,in the low level of adding a fish meal feed(15%)of threonine,to improve the triploid steelhead larval growth characteristics,digestive enzyme activity,promote the intestinal morphology development and enhance the immune ability all have positive effects.2.Study on dietary arginine requirement of triploid O.mykissArginine was added into diets to prepare 5 isoenergetic diets with arginine levels of0.86%,1.65%,2.10%,2.85% and 3.50%.Five experimental groups were set up and 450 fish were randomly divided into 15 aquariums with 3 replicates in each experimental group.By analyzing the experimental data available: at the end of the test,triploid steelhead young fish weight gain rate,specific growth rate and protein efficiency are increased with the increase of level of arginine in feed increased significantly(P <0.05);Quadratic regression model was used to fit the content of arginine in feed and SGR,and the optimal arginine level was suggested to be 2.48%(5.97% of dietary protein)to the feed of juvenile triploid O.mykiss.Moreover,although the level of arginine in feed increased gradually,but the whole fish crude fat and crude ash content in experimental group was no significant difference(P>0.05),and the crude protein content is subsequently rise trend,water is decreased significantly(P<0.05),while water content was significantly decreased(P<0.05).Dietary arginine supplementation had significant effects on amino acids except aspartic acid(Asp)(P<0.05).Superoxide dismutase(SOD),hydrogen peroxide and lysozyme in serum and liver were significantly increased and then decreased with arginine level(P<0.05),while malondialdehyde(MDA)was significantly decreased.Intestinal amylase and lipase were significantly increased,but trypsin was not significantly different(P>0.05).Muscle thickness and villus height were significantly increased in 2.85% group,and the morphology of intestinal tissue was the best.TOR reached the maximum value at 2.86%,TGF-1 and S6K1 at 2.11%.The levels of il-1 β,IL-6 and IL-8 decreased and reached the lowest values in 3.5% and 2.85% groups.The expression of TNF-α decreased first and then increased with arginine level.Both TGF-β and IL-10 reached the maximum values in the 2.85% group with the decrease and then increase of arginine level.NF-κB showed an opposite trend and reached the lowest value in 3.5% group(P<0.05).The results showed that low fish meal diet(15%)supplemented with the optimal level of arginine had positive effects on the growth,serum antioxidant,digestive physiology and immune enhancement of juvenile triploid O.mykiss and promoted its growth.