Effect of dietary soybean meal replacing fish meal and supplemented with arginine on digestion and intestinal structure of grouper in Epinephelus malabaricus
CHEN Siqi;CHENG Zhenyan;AN Maolin;FANG Zhenzhen;WANG Qingkui;Tianjin Key Lab of Aqua-Ecology and Aquaculture,College of Fisheries,Tianjin Agricultural University;
A 3×3 double-factor experiment was conducted to evaluate the effects of dietary arginine level on the digestion ability,and intestinal structure of grouper in Epinephelus malabaricus under circumstance of dietary fishmeal protein replaced by soybean meal protein. Nine isonitrogenous(crude protein 50%) and isoenergetic(20 kJ/g) experimental diets were formulated to contain three replacement levels of fishmeal protein by soybean meal(20%,30% and 40 %,respectively) and three arginine supplemental levels(0%,0.5% and 1%,respectively).Each diet was randomly assigned to three replicates,and each replicate had 50 E.malabaricus with the average body weight of(47.91±3.54) g.The experiment lasted for 70 days. The results showed that the interaction of replacement levels of fishmeal by soybean meal and arginine supplemental levels had significant effects on the activities of protease foregut and hindgut,activities of amylase of midgut,activities of lipase of hindgut,the thickness of the muscle layer and the height of the fold of the midgut and foregut of E.malabaricus.With the increasing of replacement level,the activity of protease and the fold height of hindgut increased firstly,then reduced significantly,but the muscle layer thickness of hindgut reduced significantly.With the increasing of dietary arginine,the protease activity of foregut and midgut increased firstly and then decreased. When dietary arginine was 0%,the protease activity at 30% soybean meal replacement level was 85.1% higher than that at20% replacement level,and which was 174% higher than that at 40% replacement level.The thickness of submucosa and muscle layer as well as the fold height of the hindgut significantly increased with the increasing dietary arginine level,and the maximum occurred at 1% arginine level,which was 29.4%,16.4% and 6.8% higher than that at 0% arginine level,respectively.In conclusion,the optimal replacement level was no more than 30%and arginine supplemented level was 0.5% ～ 1%,which was better for E. Malabaricus.