Effects of Dietary Gamma Aminobutyric Acid on Growth Performance, Antioxidant Status, and Feeding-related Gene Expression of Juvenile Grass Carp, Ctenopharyngodon idellus

Gamma aminobutyric acid (GABA) is one of the inhibitory neurotransmitters that may have the ability to regulate the appetite. This study aimed to evaluate the effects of dietary GABA, as a feed additive, on growth performance and antioxidant status of juvenile grass carp. Five isonitrogenous and isoenergetic experimental diets with graded levels of GABA (0, 20, 50, 100 and 200 mg/kg) were fed to grass carp juveniles (mean weight: 2.0 g) for 8 wk. The results showed that the specific growth rate (SGR) increased significantly with dietary GABA level up to the 100 mg/kg diet, and then decreased in the 200 mg/kg group (P < 0.05). The difference in SGR value between the 50 and 100 mg/kg groups was not statistically significant (P > 0.05). The survival rate was not significantly affected by dietary GABA level (P > 0.05). No significant difference was observed in the whole body composition among treatments (P > 0.05). The hepatopancreatic glutathione peroxidase (GPx) activity increased significantly (P < 0.05) with the GABA level, peaked in the group with GABA 100 mg/kg, and then decreased. The hepatopancreatic superoxide dismutase and total antioxidant capacity activities showed the same trend as GPx. Inversely, the hepatopancreatic malondialdehyde content decreased first and then increased with the dietary GABA level (P < 0.05). No significant differences were observed in the gene expression of neuropeptide Y (NPY), cholecystokinin, leptin, and ghrelin in the hepatopancreas among groups. However, the NPY and ghrelin mRNA expression levels in the brain increased significantly with the GABA level, peaked in the groups of 50 mg/kg, and then showed a decreasing trend. On the basis of quadratic regression analysis of SGR, the optimum content of dietary GABA in juvenile grass carp is suggested to be a 87.5 mg/kg diet.