A 10-week feeding trial was conducted to investigate effects of lysine on growth,physiological and biochemical indexes of blood and essential amino acids of plasma in juvenile Megalobrama amblycephala.Six isonitrogenous and isoenergetic semi-purified diets were formulated to contain graded dietary lysine levels,and the values were 1.29%,1.71%,2.09%,2.48%,2.88% and 3.27%,respectively.At the initiation of experiment,fish［(3.34±0.03)g］were randomly chosen and sorted into eighteen cages with 30 fish per cage.Each experimental diet was randomly assigned to triplicate cages in a completely randomized design.At the end of feeding trial,final body weight(FBW),weight gain rate(WRG),specific growth rate(SGR),Nitrogen retention efficiency(NRE),protein productive value(PPV)and protein efficiency ratio(PER)of fish fed diet containing 2.48% lysine were significantly higher than those fish fed 1.29% lysine diet while feed conversion ratio(FCR)showed an adverse tendency,but no significant difference was observed in survival rate(SR)of fish fed different dietary methionine levels.Increased crude protein and reduced viscerosomatic ratio(VR)were observed in fish fed 2.48% lysine diet.Ash of whole body of fish fed 2.88% and 3.27% lysine diet was higher than those fish fed 1.29% lysine diet.Alanine aminotransferase(ALT)and total protein(TP)contents were significantly improved with increasing lysine levels up to 3.27%.Urea content in plasma of fish fed 2.94% lysine diet was lower than those fish fed 1.29% lysine diet.Fish fed the 2.88% lysine diet demonstrated a significant improvement in plasma lysine content and total essential amino acid except for Leu and Val.On the basis of SGR and PPV,the optimum dietary lysine requirement of juvenile M.amblycephala was estimated to be 2.36% of diet(6.94% of protein)and 2.22% of diet(6.53% of protein),respectively,using broken-line regression analysis.