Effects of lysine on growth,physiological and biochemical indexes of blood and essential amino acids of serum in juvenile blunt snout bream(Megalobrama amblycephala)

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 w ere formulated to contain graded dietary lysine levels,and the values w ere 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]w ere randomly chosen and sorted into eighteen cages w ith 30 fish per cage. Each experimental diet w as randomly assigned to triplicate cages in a completely randomized design. At the end of feeding trial,final body w eight( FBW),w eight 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 w ere significantly higher than those fish fed 1. 29% lysine diet w hile feed conversion ratio( FCR) show ed an adverse tendency,but no significant difference w as observed in survival rate( SR) of fish fed different dietary methionine levels.Increased crude protein and reduced viscerosomatic ratio( VR) w ere observed in fish fed 2. 48% lysine diet.Ash of w hole body of fish fed 2. 88% and 3. 27% lysine diet w as higher than those fish fed 1. 29% lysine diet. Alanine aminotransferase( ALT) and total protein( TP) contents w ere significantly improved w ith increasing lysine levels up to 3. 27%. Urea content in plasma of fish fed 2. 94% lysine diet w as low er 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 w as 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.