Abstract:In this study, the effect of Vallisneria natans meal used as feed ingredient in the diet of grass carp (Ctenopharyngodon idellus) on growth, physiological, and biochemical properties was evaluated. Four isonitrogenous and isoenergic diets were formulated by replacing the secondary powder and rice bran with 0 (VN0, control), 10% (VN1), 20% (VN2), and 30% (VN3) V. natans meal. In addition, a group that was fed only with fresh V. natans was designed. Juvenile grass carp of initial weight (18.85±0.20) g were selected to be cultured for 56 days in indoor cement tank cages. The results showed that addition of V. natans meal did not affect the growth performance, survival rate of grass carp, and feed coefficient. With the increase in the amount of V. natans meal, the visceral index and hepatopancreas index significantly decreased, the activity of amylase in the foregut was significantly increased, and that in the middle and rear intestines was significantly decreased. In the control group, the protease activity of foregut, and middle and rear intestines, in turn, strengthened, and with the increase in the content of V. natans meal the activity of foregut protease was significantly increased; meanwhile, midgut proteinase activity increased first, then decreased, and increased again. The highest value was observed in group VN1, and protease activity in the posterior intestine showed a significant decrease trend. The superoxide dismutase (SOD) activity of the hepatopancreas was significantly increased, whereas malondialdehyde (MDA) content decreased first and then increased, and that in group VN3 was the highest. The content of serum total protein increased significantly, whereas the serum albumin content increased first and then decreased, and the highest value was found in group VN1. Compared with the control group, serum alanine aminotransferase (ALT) activity increased and then recovered to the control level, and serum aspartate aminotrasferase (AST) activity significantly decreased in V. natans meal groups, and there was no significant difference among the V. natans meal groups. The addition of V. natans meal resulted in significantly reduced apparent digestibility of the diets and enhanced resistance ability of grass carp to Aeromonas hydrophila to some extent. Group VN showed negative growth and depressed visceral index, hepatopancreas index, serum albumin, globulin, and ALT. The activity of amylase in the intestinal segments was significantly higher than that in all practical formulated diets. The activity of midgut protease in VN group was significantly higher than that in the control group, and that of hindgut protease was significantly lower than that of the control group. The above results showed that the addition of 10%~30% V. natans meal in the diet had no effect on the growth of grass carp, but was beneficial to the health of the fish body. The results indicated that V. natans meal used as the raw material of grass carp feed for resource utilization would be much better than fresh V. natans.
