Proanthocyanidins are polyphenol compounds that can be found in some plants and their fruits. In this study, the effects of grape seed proanthocyanidin extract (GSPE) as a dietary antioxidant supplement were evaluated on growth performance, serum biochemical properties (including glucose, cholesterol, and triglyceride), fillet proximate composition (crude protein, lipid, moisture, and ash), and liver antioxidant enzyme activity in common carp fingerlings. The experimental diets including five groups with different concentrations of GSPE (200, 400, 600, 800, and 1500 mg per kilogram of diet), along with a control group (0 mg GSPE per kilogram of diet), were used during forty days of experimentation. The orthogonal regression analysis revealed a linear trend for final weight (P < 0.05, R2 = 0.62) and cubic trends for weight gain (P < 0.05, R2 = 0.52), specific growth rate (P < 0.05, R2 = 0.52), condition factor (P < 0.05, R2 = 0.77), and food conversion ratio (P < 0.05, R2 = 0.50). The serum glucose, cholesterol, and triglyceride levels in the GSPE treatment groups significantly decreased with respect to those in the control group (P < 0.05). Fillet protein content was significantly higher in the G200 group than in the control group (P < 0.05); however, there was no difference between the fat, ash, and moisture contents of the experimental and control fish. Superoxide dismutase and glutathione peroxidase activity significantly increased in G200 with respect to that in the control group (P < 0.05). Catalase activity, however, decreased in the GSPE treatment group livers with compared to that of the control group (P < 0.05). Dosedependent effects of GSPE were observed in growth performance, serum biochemical parameters, body proximate composition, and liver first-line antioxidant defense system in common carp; however, the level of 1500 mg GSPE per kilogram of diet gave reverse response for some examined parameters. Overall, a low level of dietary inclusion of GSPE was found to be somewhat effective on carp growth performance, serum biochemical adjustment, fillet protein content, and liver antioxidant defense, and it may therefore be used as an important feed supplement in carp production.
