Effects Of Tryptophan In Two Protein Levels Diets On Feed Intake, Growth Performance, And Immunity Of Litopenaeus Vannamei

The experiment was conducted to study the effects of tryptophan in two protein levels diets on feed intake,growth performance,biochemical indices, digestive enzymes, immunity function, antioxidant capability and 5-HT metabolism related substancesof Litopenaeus Vannamei.Nine hundred and sixty Litopenaeus Vannamei with an aninitial body weight of 1.95±0.01 g were randomly divided into 6 groups, each with 4 replicates of 40 shrimps, and fed diets supplemented with 0, 2500 and 10000 mg/kg of tryptophan in 43.6% and 40.8% protein diets(soybean meal and peanut meal as the main protein source) respectively. The feeding trial lasted for 56 days. At the end of the feeding trial, shrimps were fasted for 24 h, then each group was counted and weighed.The samples were collected for analysis. The contents and results were as follows: 1. Effects of tryptophan in two protein levels diets onfeed intake and growth performance of Litopenaeus vannameiFeed conversion rate(FC) in Litopenaeus vannameifed with high protein diets(43.6%)was significantly lower than that of low protein diets(40.8%)(P<0.05). Feed intake(FI) and daily feed intake(DFI) of shrimp fed with low protein diets were significantly higher than that of highprotein diets(P<0.05), the feed intake in 2500 and 10 000 mg/kg tryptophan groups was significantly higher than the control group(P<0.05). The results showed that survival rates(SR) of shrimp fed with high protein diets was significantly lower than thatof low protein diets(P<0.05), while weight gain rate(WGR) and specific growth rate(SGR) of shrimp fed with high protein diets were significantly higher than of low protein diets(P<0.05). The survival rate, terminal average weight, weight gain and specific growth rate had no significant difference under different proteinand tryptophan levels(P>0.05). Hepatopancreas index had no significant differenceunder different protein and tryptophan levels(P>0.05). Crude protein, crude fat, moisture, crude ash contents were not significantly influencedat different protein and tryptophan levels of Litopenaeus vannamei(P>0.05).The results indicate that tryptophan could improve feed intake, and that had no significant effects on the growth performance and body composition of shrimp of Litopenaeus vannamei. 2. Effects of tryptophan in two protein levels diets on biochemical indices and digestive enzymes activities of Litopenaeus vannameiSerum triglycerides content of shrimp fed with high protein diets was significantly higher than that of low protein diets(P<0.05), while the influenceamong different tryptophan levels had no significant difference(P>0.05). Glutamic pyruvic transaminase of hepatopancreas had interaction at different protein and tryptophan levels(P<0.05), and aspartate aminotransferase activity of 2 500,10 000mg/kg tryptophan groups was significantly higher than the control group(P<0.05). Hepatopancreas amylase activitiesin 2 500,10 000 mg/kg tryptophan groups was significantly higher than the control group(P<0.05), and hepatopancreasprotease activity in 10 000mg/kg group was significantly higher than the control group(P<0.05).The intestinal protease activity of shrimp fed with low protein diets was significantly higher than that of high protein diets(P<0.05). The results indicate that but tryptophan could improvedigestive enzymes activitiesand hepatopancreas alanine aminotransferase activity of shrimp on interaction of protein and tryptophan levels.3. Effects of tryptophan in two proptein levels diets onimmuneindices and antioxidantindices of Litopenaeus vannameiThe results showed serum nitric oxide synthase activity of shrimp fed with high protein diets was significantly higher than that of low protein diets(P<0.05), and that in 0, 10 000mg/kg tryptophan groups was significantly higher than that in 2 500mg/kg tryptophan group(P<0.05). Serum acid phosphatase activity had interaction on protein and tryptophan levels diets(P<0.05). Hepatopancreas oxide synthase activity of shrimp fed with low protein diets was significantly higher than that of high protein diets(P<0.05), and alkaline phosphatase activity had interaction on protein and tryptophan levels(P<0.05). Serum total antioxidant capacity in 0, 2 500mg/kg tryptophan groups was significantly lower than that in 10 000mg/kg tryptophan group(P<0.05).Malondialdehyde content of 2 500mg/kg tryptophan group was significantly lower than that of 0, 10 000mg/kg tryptophan groups(P<0.05).Hepatopancreas pancreas catalase activity a of shrimp fed with high protein dietswas significantly higher than of low protein diets(P<0.05), and the controlgroup was significantly higher than that in 2 500,10 000mg/kg tryptophan groups(P<0.05), which was an interaction(P<0.05). Hepatopancreas malondialdehyde content in 10 000mg/kg tryptophan group was significantly higher than the control group(P<0.05). The results indicate that tryptophan in two protein levels dietscould increase the immunity and antioxidant capability of shrimp. 4. Effects of tryptophan in two protein levels diets onserotonin metabolism-related substance of Litopenaeus vannameiThe results showed that TPH, 5-HT, NPY content in serum, intestine and brain of shrimpwere not significantlyaffectedby tryptophan and protein levels(P> 0.05).At 43.6% protein levels, TPH, 5-HT content in serum showed a gradual upward trend,while NPY content showed increased and then decreased trendwith increasement of tryptophan. TPH, 5-HT, NPY levels in brain rise firstly, then decreased with increasement of tryptophan. At 40.8% protein levels, the intestinal TPH, NPY content was firstly increased and then decreased with increasement of tryptophan. The results indicate that tryptophan had no significant effect on the 5-HT metabolism-related substances contents ofshrimp.