Effects of diet α-ketoglutarate (AKG) supplementation on the growth performance, antioxidant defense system, intestinal digestive enzymes, and immune response of grass carp (Ctenopharyngodon idellus)

Abstract

This study was conducted to investigate the effects of diet 7.5 g/kg α-ketoglutarate (AKG) on the growth performance, antioxidant defense system, digestive enzymes, and immune response of grass carp (Ctenopharyngodon idellus). A total of 400 grass carp with an average body weight 10.81 ± 0.68 g was randomly allocated into 2 groups with 4 replicates of 50 fish respectively. The experiment was conducted in net cages (1.5 m × 1.5 m × 1.5 m) suspended in an indoor cement pool. Fish were fed a basic diet containing either 0 (control) or 7.5 g/kg AKG (supplemented diet). The experiment lasted for 8 weeks (56 days). Results indicated that compared with the control group, the final weight (FW), weight gain rate (WGR), specific growth rate (SGR), and protein efficiency ratio (PER) in the AKG group were increased significantly (P < 0.05). However, the feed conversion ratio (FCR) was decreased significantly (P < 0.05). The 7.5 g/kg AKG supplementation significantly increased the activities of glutamine synthetase (GS), glutathione peroxidase (GSH-Px), catalase (CAT), total superoxide dismutase (T-SOD), and hexokinase (HK), as well as the concentrations of glutathione (GSH), total antioxidant capacity (T-AOC), and complement 3 (C3) in blood (P < 0.05), while significantly decreased the concentrations of malondialdehyde (MDA) and hemoglobin (Hb) (P < 0.05). The GS activity and GSH concentration in hepatopancreas were increased significantly (P < 0.05), whereas the glycogen concentration in hepatopancreas, and the glycogen concentration and GS activity in the muscle were significantly decreased (P < 0.05). In addition, 7.5 g/kg AKG supplementation significantly increased the concentration of GSH and the activities of amylase, protease, and lipase in fore-gut, alkaline phosphates (ALP) in the mid-gut, and Na-ATP and Ca-ATP in the gill (P < 0.05), as well as γ-glutamyl transpeptidase (γ-GT) both in fore-gut and mid-gut (P < 0.05), whereas the activity of acid phosphatase (ACP) in the mid-gut was decreased significantly (P < 0.05). In conclusion, diet 7.5 g/kg AKG supplementation in grass carp may improve the growth performance and immune response and play crucial roles in regulating the activities of GS, antioxidant defense system, and digestive enzymes.