| Macrobrachium nipponense,commonly known as oriental river prawn,is one of the main economic species of freshwater shrimp culture in China because of its rapid growth,short culture cycle and miscellaneous feeding habits.With the continuous expansion of the culture scale and the increasing artificial formula feed amount on M.nipponense,its nutrient requirement has attracted more and more attention of scholars at home and abroad.At present,it mainly focuses on the demand of macronutrients such as protein,fat and carbohydrate,but few studies are on essential amino acids.Tryptophan is the third limited essential amino acid for most aquatic animals.It has a variety of physiological functions,such as regulating growth,participating in protein synthesis,nutrition and metabolism,relieving oxidative stress,improving immunity and regulating fighting behavior.Meanwhile,the requirement of essential amino acids on M.nipponense was reported only in lysine and methionine,while the suitable demand for tryptophan has not been reported.In this experiment,six different levels of tryptophan were added to form isonitrogenous and isolipidic formuated feed to determine the suitable amount of tryptophan on M.nipponense.According to the optimal addition amount obtained from the growth feeding trail,low,medium and high tryptophan levels were selected to obverse the fighting behavior of M.nipponense.The effect of tryptophan level in feed on 5’-hydroxytryptamine and fighting behavior of M.nipponense was analyzed in order to provide reference for the development of specialized commercial feed for M.nipponense.1 Effects of tryptophan on growth performance,body composition,muscle amino acid,hemolymph biochemical index and hepatopancreatic antioxidant index of M.nipponenseSix isonitrogenous and isolipidic feeds were formulated with fishmeal,gelatin,soybean meal,corn gluten meal and amino acid mixture as protein source,fish oil and soybean oil as lipid source,and α-starch as carbohydrate.The supplement levels of tryptophan in each group were 0,0.15%,0.30%,0.45%,0.60% and 0.75% respectively.The true levels of tryptophan in each group were 0.07%,0.17%,0.29%,0.39%,0.52% and 0.64% respectively based on detection.Four replicates of M.nipponense were randomly assigned for each experimental feed.After 8 weeks,the growth performance and hepatopancreas antioxidant enzyme activity of M.nipponense were analyzed.Compared with 0.07% tryptophan group,there was no significant difference on the survival rate and the final body weight(FW)among all groups(P>0.05),while the FW of the prawns fed feed with 0.29% tryptophan reached the maximum.With the increase of tryptophan level in feed,the weight growth rate(WGR)of M.nipponense increased first and then decreased.The WGR and specific growth rate(SGR)of prawns fed feed with 0.07%tryptophan were significantly lower than those of other groups(P<0.05),and the WGR and SGR of the prawns fed with 0.29% tryptophan were higher than those of other experimental groups.The protein efficient rate(PER)of M.nipponense increased first and then decreased.Compared with the control group(0.07% tryptophan level),the PER of prawns fed feeds with0.17%,0.29%,0.39% and 0.52% tryptophan was significantly increased(P<0.05),with the highest value in 0.39% group.There was no significant difference on PER between the prawns fed feed with 0.07% and 0.64% tryptophan levels(P>0.05).With the increase of tryptophan level in feed,the Feed conversion rate(FCR)of M.nipponense decreased first and then increased.Compared with 0.07% tryptophan group,the FCR of prawns fed feeds with 0.17%,0.29%,0.39% and 0.52% tryptophan decreased significantly(P<0.05),of which0.39% group was the lowest,while the FCR of prawns in 0.64% tryptophan group were not significantly different with that in the control group(P>0.05).Compared with 0.07%tryptophan group,the feed intake(FI)of prawns in 0.39% tryptophan group decreased significantly(P<0.05),but there was no significant difference among other groups(P>0.05).Based on protein efficiency and feed coefficient,the suitable addition amount of tryptophan in M.nipponense feed was 0.37%,accounting for 0.95% of feed protein,according to quadratic regression analysis.With the increasing tryptophan level in feed,there was no significant difference in moisture among all groups(P>0.05).Compared with 0.07% tryptophan group,the crude protein content of M.nipponense in 0.17%,0.29% and 0.52% tryptophan groups increased significantly(P<0.05),while the crude protein content in 0.39% tryptophan group decreased significantly(P<0.05).The crude protein content of M.nipponense fed with 0.29%tryptophan was the highest.The crude lipid content of prawns in 0.52% and 0.64%tryptophan groups was significantly higher than that in 0.17% and 0.39% groups(P<0.05).The ash content of prawn in the 0.64% tryptophan group was significantly higher than that in the 0.39% group(P<0.05),but there was no significant difference among the other groups(P>0.05).Dietary tryptophan had no significant effects on single amino acid content,total essential amino acid content,total non-essential amino acid content and total amino acid content of M.nipponense muscle(P>0.05).Compared with 0.07% tryptophan group,the content of total protein content(TP)in 0.64%tryptophan group was significantly increased(P>0.05),and there was no significant difference among other groups(P>0.05).The total cholesterol content(TC)in 0.64%tryptophan group was significantly higher than that in 0.17% group(P<0.05).The triglyceride content(TG)in hemolymph of M.nipponense fed feed with 0.29% tryptophan was significantly higher than that of prawns in 0.17%,0.52% and 0.64% groups(P<0.05),but there was no significant difference among other groups(P>0.05).When dietary tryptophan content was higher than 0.29%,the haemolymph glucose content(Glu)in M.nipponense gradually decreased with the increasment of tryptophan level.Compared with0.07% tryptophan group,the Glu contents in 0.17%,0.39%,0.52% and 0.64% tryptophan groups were significantly decreased(P< 0.05).The Glu in 0.29 % tryptophan group was decreased,not significant difference(P>0.05).The urea nitrogen content(UN)in 0.29% and0.39% tryptophan groups was significantly lower than that in 0.64% group(P<0.05).Compared with 0.07% tryptophan group,the Superoxide dismutase activity(SOD)was significantly higher(P<0.05).The SOD activity of M.nipponense fed diet with 0.39%tryptophan reached the peak.Compared with 0.07% tryptophan group,the … content(MDA)in 0.52% and 0.64% tryptophan group decreased significantly(P<0.05),and the MDA content in other groups decreased without significant difference(P>0.05).2 Effects of tryptophan on fighting behavior,5-HT content in hemolymph and expression of 5-HT1 B receptor in hepatopancreas of M.nipponense before and after fightingIn order to study the effect of dietary tryptophan on the fighting behavior of M.nipponense,low,medium and high tryptophan levels(supplemented with 0,0.30% and 0.75%,respectively)were choosen according to the results of previous growth experiments.After 8weeks of feeding trail in the glass tanks system,the fighting behavior was observed and analyzed.The measured levels of tryptophan in each group were 0.06%,0.27% and 0.60%,respectively.Four replicates of M.nipponense were randomly assigned to each experimental feed.After 8 weeks,the fighting behavior,the content of serotonin in hemolymph and the expression of 5-HT1 B receptor in hepatopancreas were analyzed.The increase of tryptophan in diet significantly decreased the times of approach,contact and fighting of M.nipponense(P>0.05)with a decreasing trend.Compared with 0.06%tryptophan group,prawns in 0.27% and 0.60% tryptophan groups significantly reduced the times of proximity and contact(P<0.05).The fighting frequencies and fighting time of the prawns in the 0.60% tryptophan group were lower than those in the 0.29% group,but the difference was not significant(P>0.05).The content of 5-HT in hemolymph of M.nipponense increased significantly after fighting than that before fighting(P<0.05),which was not significantly correlated with the tryptophan content in diet.Before fighting,compared with 0.06% tryptophan group,the 5-HT content in hemolymph of prawns in 0.27% and 0.60% tryptophan groups increased significantly,and that in 0.60% group was significantly higher than that in 0.27% group(P<0.05).After fighting,compared with 0.06% tryptophan group,the 5-HT content in hemolymph of prawns in 0.27% and 0.60% tryptophan groups increased significantly,and that in 0.60% group was significantly higher than that in 0.27% group(P<0.05).The expression of 5-HT1 B receptor in hepatopancreas of M.nipponense increased significantly after fighting than that before fighting(P<0.001).There was no significant correlation with the dietary tryptophan content.Before fighting,compared with 0.06%tryptophan group,the expression of hepatopancreatic 5-HT1 B receptor in 0.27% and 0.60%tryptophan group was significantly higher than that in 0.27% group(P<0.05).After fighting,compared with 0.06% tryptophan group,the content of 5-HT in hemolymph of prawns in0.27% and 0.60% tryptophan groups increased significantly,and that in 0.60% group was significantly higher than that in 0.27% group(P<0.05).To sum up,appropriate tryptophan can improve the growth performance of M.nipponense,increase the whole-body crude protein and lipid,while excessive tryptophan would inhibit the growth to a certain extent.Appropriate tryptophan could increase antioxidant enzyme activities such as SOD,reduce the MDA content and enhance the antioxidant capacity of M.nipponense.Based on protein efficiency ratio and feed coefficient,the suitable tryptophan of M.nipponense was 0.37%,accounting for 0.95% of feed protein.The tryptophan supplement could reduce the times of approach,contact and fighting of M.nipponense,and reduce the fighting time.The tryptophan addition could increase the 5-HT content in hemolymph and 5-HT1 B receptor gene expression level in hepatopancreas of M.nipponense in a dose-dependent manner. |
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