Study Of Interactive Effect Of Dietary Leucine And Isoleucine On Japanese Flounder Paralichthys Olivaceus

Japanese flounder Paralichthys olivaceus is an important marine fish species in north China.The nutrition requirement study of this species has made abundant achievements at present.But the interactive effects of amino acids on Japanese flounder is not sufficient,especially the branched chain amino acids.This study was designed containing 2 Leucine(Leu)levels combined with 3 Isoleucine(Ile)levels as a 2×3 experimental design to determine the interactive effects of Leu and Ile on growth performance,blood,immune,muscle amino acid profiles etc.on Japanese flounder.To provide a rational proportion of amino acid and improve the relationship between the branched chain amino acids for further study of formula feed on Japanese flounder.The experiment was formulated based on the juvenile Japanese flounder amino acid profile of 50% fish whole body protein.Six experimental diets containing 2 Leu levels(2.58 and 5.08% of dry diet,analyzed values)combined with 3 Ile levels(1.44,2.21 and 4.44% of dry diet,analyzed values)as a 2×3 experimental design(LL-LI,LL-MI,LL-HI,HL-LI,HL-MI,HL-HI).A 60-day feeding trial was conducted in the same conditions with initial weight of 1.73±0.01g(mean ± S.E.M)randomly divide into six groups(each treatments 3 repeat).And total of 18 blue circular polyethylene tank.The result discovered that relatively higher growth parameters(FBW,BWG and SGR)were found in feed LL-HI.Besides,interactive effects were found on muscle valine,methionine and phenylalanine.And both dietary Leu and Ile supplementation were significant factors on muscle amino acids profiles(except histidine and lysine).Moreover,no interactive effects were observed and neither dietary Leu nor Ile was a significant factor on blood parameters,except for plasma total protein concentration which has been significantly affected by dietary Leu.This study suggested that when growth parameters were considered,stimulatory effects were found on growth parameters in the low dietary Leu groups,besides,antagonistic effects were observed in the high dietary Leu groups.Overall,the best growth performance of test fish would be LL-HI and HL-LI diets.After the feeding trial,intestine digestive enzymes(Protease and Lipase)and liver immune-related enzymes(T-AOC,CAT,SOD,ACP,AKP)activities of test fish were measured.The result showed that high dietary Leu can reduce the activity of intestine digestive enzymes(except LI),and dietary Ile can significantly(P < 0.05)increase the digestive enzymes of intestine(except LI).And in low Leu groups,when dietary Ile ? 2.21%,the activities of liver CAT,SOD and ACP as well as AKP can significantly increased(P < 0.05).But in high Leu groups,when the level of Ile ? 2.21% in the dietary,the activities of CAT,SOD and AKP can significantly decreased(P < 0.05).It can be concluded that the interactive effect of dietary Leu and Ile can significantly affect the intestine digestive enzyme activities as well as part of immune enzyme activities of Japanese flounder.And fish fed with low Leu(2.58%)and high Ile(4.44%)diet(LL-HI)showed higher tissue enzyme activities of Japanese flounder.After the feeding trial,the skin mucus lysozyme activity of Japanese flounder was detected.And the results showed that the different level of Leucine and Isoleucine diet can significantly affect skin mucus lysozyme activity.And the skin mucus lysozyme activity was found the highest when fed low Leu with low Ile diets(LL-LI).After 60 days feeding,the low salinity stress tolerance of Japanese flounder was detected.The results showed that the different dietary treatments can significantly affect the low salinity stress tolerance.And fed with high Leu with high Ile levels of diet(HL-HI)showed the highest low salinity stress tolerance(LT50)of Japanese flounder,which illustrated the best low salinity resistance.