In order to estimate the appropriate protein to lipid(P/L)ratio of blunt snout bream(Megalobrama amblycephala)for semi-purified diet in different growth stages,2 feeding trials including diets with different P/L levels were conducted in the same formula system.Casein and Peruvian fish meal were used as the source of protein,while soybean oil and soy lecithin were used as lipid source.Dietary protein concentration ranged from 26.93% to 35.65%,and the lipid concentration range was correspondingly between 10.24% and 3.35%.The experimental diets contained 6 gradients,and P/L ratios were 2.63,3.20,4.07,5.33,7.25,10.64,respectively.Test one,two respectively used blunt snout bream with initial average weight of (35.07±0.45) g(juvenile stage),(101.65±1.82) g(premature stage),and were divided into 6 groups,each with 4 replicates.Experiments on the two tests were conducted in pond cages.Both the two tests were fed with the above-mentioned feed,precisely and on schedule.The feeding time were respectively 85 d,and 56 d.The results of 2 experiments showed that:with the feed P/L ratio gradually increased,the evaluation indexes such as the specific growth rate(SGR),the rate of protein deposition(PDR)and energy retention(ERR)increased first and then decreased.The feed conversion ratio(FCR)was the first decline after rising trend.The best growth appeared in the group of P/L 5.33.SGR,FCR,PDR and ERR were used as sensitive criterions for regression analysis,and it showed that different growth stages of blunt snout bream need different optimal P/L ratios:Appropriate P/L ratio of juvenile stage was 6.09-7.58,the optimal protein concentration was 32.83%-33.98% and lipid concentration was 4.48%-5.39%;In the conditions of the average daily intake of 5.06 g/100 g body weight,protein requirement was 1.66-1.72 g/100 g body weight,and lipid requirement was 0.23-0.27 g/100 g body weight for juvenile stage.Appropriate P/L ratio of premature stage was 4.03-4.34,the optimal protein concentration was 30.19%-30.72% and lipid concentration was 7.07%-7.49%.In the conditions of the average daily intake of 3.61 g/100 g body weight,protein requirement was 1.09-1.11 g/100 g body weight,and lipid requirement was 0.26-0.27 g/100 g body weight for premature stage.