Effects Of Leucine On Production Performance,Muscle Growth And Flesh Quality Of Hybrid Bagrid Catfish

The aim of the experiment was to investigate the effects of dietary leucine（Leu）levels on production performance,muscle growth and flesh quality of hybrid bagrid catfish.A total of 630 hybrid bagrid catfish（Pelteobagrus vachelli×Leiocassis longirostris）with average initial weight 23.0±0.2 g were randomly assigned to seven treatments with with 3 replicates per treatment,and 30 fish per replicate.Fish were fed seven diets contained with 10.0（control）,15.0,20.0,25.0,30.0,35.0 and 40.0 g Leu kg^-1diet for 8 weeks.The results are as follows:1.Effects of Leu on production performance and muscle growth of hybrid bagrid catfishAfter 8-week feeding trial,the results showed that optimal dietary Leu level significantly increased the percent weight gain（PWG）,specific growth rate（SGR）,food intake（FI）,feed efficiency（FE）,protein efficiency ratio（PER）,crude protein content,crude fat content,protein production value（PPV）,and lipid production value（LPV）（P<0.05）.The moisture,crude ash content,and ash production value（APV）of fish whole body were were not significantly affected by Leu supplementation（P>0.05）.Optimal dietary Leu level significantly increased the muscle fiber diameter and muscle fiber density（P<0.05）.Optimal dietary Leu level significantly increased the genes expression of MRFs、MSTN、PCNA and MHC in muscle（P<0.05）.2.Effects of leucine on flesh quality of hybrid bagrid catfishAfter 8-week feeding trial,the results showed that optimal dietary Leu level:（1）significantly increased the shear force,haedness,gumminess,chewiness,springiness and hydroxyproline content（P<0.05）,but decreased the cooking loss,lactate content,and cathepsin B and L activities in muscle of hybrid bagrid catfish（P<0.05）.（2）significantly increased the muscle protein content（P<0.05）（3）significantly up-regulated the genes expression of IGF-I,IGF-IR,PI3K,and TOR,but down-regulated the 4E-BP1,FOXO1,FOXO3a,MURF-1,and MAFBX m RNA levels（P<0.05）.No significant difference was found in AKT and S6K1 m RNA expression of muscle were observed among treaments（P>0.05）.（4）significantly decreased the ROS and PC contents（P<0.05）,and increased the activities of SOD,CAT,GPX,GST,GR,and GSH content in muscle（P<0.05）.There was not significant difference in the mscle MDA content with different dietary Leu levels（P>0.05）.（5）significantly improved the genes expression of SOD,CAT,GPX,GST and GCLC in muscle（P<0.05）,and decreased the Keap1 m RNA expression（P<0.05）.In summary,the present work showed that optimal dietary Leu level improved production performance,muscle fibers diameter and density of hybrid bagrid catfish.In addition,optimal dietary Leu level may improved the proliferation and differentiation of myogenic progenitor cells by regulating MRFs,MSTN,PCNA,and MHC gene transcriptions,and then induce muscle growth.Moreover,optimal dietary Leu level was effective in elevating flesh quality of hybrid bagrid catfish.The improvement of the flesh quality by Leu related to enhancing fish physical and protein deposition,and antioxidant capacity in muscle of hybrid bagrid catfish.Based on the quadratic regression analysis of PWG,the Leu requirement of hybrid bagrid catfish（23.0±0.2 g）were 26.45 g kg^-1diet or 68.75 g kg^-1dietary protein.