Effect of dietary grape seed extract in common sole, Solea solea.

Sole farming is hampered by poor growth and high sensitivity to stress and infectious diseases. Hence, supplementing diets with health promoting additives such as antioxidants could be worth studying to improve the growth performance of this species. Grape seed proanthocyanidin extract (GSPE), a natural polyphenolic antioxidant, has been used as a human food supplement for health promotion, but few data are available on its application in animal nutrition and none in fish. The present study was aimed at investigating the effect of supplementing a commercial dry extruded feed formulated for sole (Diet E) with GSPE at a dose of 50 mg/kg (Diet E+GSPE) on the growth performance, blood plasma lipid profile and total antioxidant activity of Solea solea. Two hundred eighty four fishes (mean weight 38.1±0.6 g) were randomly distributed in 8 rectangular troughs (0.37 m2) at 3.7 kg/m2 stocking density, and fed at 1% body weight/day over 147 days, according to a single-factor experimental design with 4 replicates per diet. Survival rate, feed conversion ratio (FCR) and specific growth rate (SGR) were calculated per group at the end of the trial, whereas plasma levels of total, HDL, LDL-cholesterol, triglycerides and total antioxidant activity were measured at days 87 and 147 on 8 fish samples per treatment. All dietary groups had similar, high survival rates (95.8 vs 97.1%, P>0.05). Diet E+GSPE resulted in a slight but significantly impaired SGR over diet E (0.28 vs 0.31, P<0.05), but in the same FCR (P>0.05). Blood lipid profile was also unaffected by the dietary treatment, while the addition of GSPE to the diet resulted in significantly increased antioxidant activity in plasma (P<0.05) suggesting the usefulness of grape seed extract in promoting resistance to oxidative stress in common sole.