Evaluation Of Vital Wheat Gluten As A Source Of Protein In Extruded Diets For Juvenile Red Spotted Grouper (Epinephelus Akaara): Feed Technological Properties And Biological Responses

This study was attempted to evaluate GWT as protein source in comparison with high-quality fish meal(Low-temperature dried fish meal,LT-FM)and soy protein concentrate(SPC)in extruded practical diet for red spotted grouper(Epinephelus akaara).Where GWT was an ingredient blend mixed by vital wheat gluten(VWG),wheat and taurine with the ratio of 77.5%,20.5%and 2.0%respectively.Eight diets had been formulated,including a control diet based on LT-FM(20.0%)and SPC(21.4%),six diets with decreasing LT-FM or SPC replaced by GWT(replaced level of 1/3,2/3 and 100%,respectively,based on dietary protrein level)and one diet with both 50%of LT-FM and SPC been replaced by GWT.Each diet had been fed to triplicate tanks of red spotted grouper with an initial weight of 9.55±0.03 g which were reared in an in-door recirculated sea water system for 56 days and the water quality parameters(water flow rate,temperature,D.O.,salinity)during the experimental period were 8-9 L/min,27.9 ~oC,6.0mg/Land 25 ppt.And the results shown,during the first 28-day,the replacement of LT-FM or SPC by GWT have no significant effect on feed intake(FI),fish weight gain(WG)and feed utilization(FCR)(P>0.05),except an obvious increase of WG(13.4±0.5g)for the diet both LT-FM and SPC replaced(P<0.05).At the end of trial,significant liner increase(P<0.05)of FI(18.7 to 24.8 g per fish),WG(15.2 to 24.1 g per fish)and significant liner decrease(P<0.05)of FCR(1.23 to 1.03)were seen when the LT-FM had been gradually replaced by GWT from 0 to 100%.Hepotasomatic index(HSI)and condition factor(CF)was not significant affected(P>0.05)with gradually LT-FM decreasing.The composition of whole body and plasma,energy retention efficiency(ERE),plasma superoxide dismutase(SOD)and liver malondialdehyde(MDA)were no significantly change with decreasing FM inclusion.However,increasing inclusion of GWT(with LT-FM deceasing)has a significant positive effect on protein retention efficiency(PRE)and activity of liver SOD(P<0.05).FI and WG were significant increased according with a second–order polynomial regression model(P<0.05),while FCR was just on the contrary(P<0.05)with SPC gradually decreasing from 0 to 100%.At the level of 2/3 SPC replaced by GWT,FI and WG had the maximum values of 25.0 g and 23.6 g correspondingly,and FCR had the minimum value of 1.07.The increase of GWT inclusion had no significant effect on HSI and CF(P>0.05).Whole body composition,plasma chemical composition,PRE,plasma SOD and liver MDA content were no significantly change with decreasing SPC inclusion(P>0.05).And a significant positive effect on liver SOD was found when the SPC had been gradually replaced by GWT from 0 to 100%.Both FI and WG were significantly increased when both 50%of LT-FM and SPC were replaced by GWT(P<0.05),while FCR was not significantly affected(P>0.05).Also,a positive anti-effect on oxidative stress had been found,with a significantly increase of SOD activity and a significantly decrease of MDA content.To conclude,in extruded practical diet of red spotted grouper with both 20.0%inclusion of high quality fish meal and 21.4%inclusion of SPC,that total LT-FM and 2/3 SPC can be safely replaced by the mixed ingredient blend GWT supplemented with Lysine,Arginine,Methionine and Threonine.