Effects of dietary protein content on growth performance and digestive enzyme activities of black tiger shrimp,Penaeus monodon

A 56-day feeding trial was conducted to study the effects of six dietary protein content(36%,38%,40%,42%,44%,46%) on growth performance(weight gain,WG;specific growth rate,SGR;survival rate,SR) and digestive enzyme activities(protease and amylase activities of hepatopancreas,stomach and intestine) of Penaeus monodon.The triplicate feeding trials were conducted in tanks indoor,and 30 prawns(initial mean weight: 1.03±0.02 g)were randomly stocked in each of eighteen 500 L tanks.The results showed that WG and SGR increased with the increasing dietary protein content,WG and SGR of shrimp fed with 40% dietary protein were significantly higher than that of shrimp fed with 36% dietary protein(P0.05),but showed no significant differences with other dietary proteins(P0.05).The maximal WG and SGR were found in 40% group(WGmax=417.35%,SGRmax=2.93%·d-1).When the protein level was 38%,the feed conversion rate was the lowest and significantly lower than that of shrimp fed with 44% and 46%(P0.05).Body protein content of shrimp fed with 44% dietary protein was the highest and significantly different from that of shrimp fed with 36%,38% and 42% dietary protein(P0.05).The apparent protein digestibility of shrimp fed with 42% dietary protein was significantly higher than that of shrimp fed with 46% dietary protein(P0.05),but showed no significant differences with other dietary protein(P0.05).Shrimp fed with high protein diets(44%,46%) had significantly lower PER values than shrimp fed with lower protein diets(36%-42%)(P0.05).The proteinase activities in hepatopancreas,stomach and intestine fluctuated from high to low with the increasing of the dietary protein content.The amylase activities decreased with the increasing of the dietary protein levels.Stomach amylase activities of shrimp fed with 38%-42% dietary protein were significantly higher than that of shrimp fed with 36% dietary protein(P0.05).Intestine amylase activity of shrimp fed with 40% dietary protein was significantly higher than that of shrimp fed with other dietary protein levels(P0.05).Based on the regression of WG to dietary protein content,the optimal dietary protein requirement for juvenile P.monodon was 39.70%.