Olive oil by-product as a natural antioxidant in gilthead sea bream (Sparus aurata) nutrition

.The aim of this work was to evaluate the efficiency of a natural antioxidant substance in gilthead sea bream (Sparus aurata) feeds. An olive oil by-product, olive mill vegetation water (VW), contains polyphenols, which have a strong antioxidant activity. A 147 days long growth trial was conducted (monofactorial balanced; 4x3) with the diet as the experimental factor. Two diets (isonitrogenous CP= 40% and isoenergetic GE = 18Mj*kg-1 on DM) were formulated with 1% and 5% of VW inclusion level (VW1, VW5), against a control diet without VW. 600 juvenile gilthead sea breams (mean body weight 114.1±5.7g) were utilised. At the end of the growth trial the productive parameters and somatic indexes were calculated. Antioxidant activity in fish fillets was investigated using TBARS and DPPH assays. Some hematological parameters and digestive enzyme patterns were measured in fish in the middle and at the end of the experiment. The TBARS values showed slight delays in the development of oxidation in the fillet of fish fed with VW. No statistical differences appeared between the fish fed with the experimental diet and the control group, except for maltase activity which increased as the VW inclusion level was increased. The use of VW in a gilthead sea bream diet did not show any detrimental effects in gilthead sea bream production and physiological parameters and slightly improved the conservation of the fish fillets.