Physiological effects of natural olive oil antioxidants utilization in rainbow trout (Onchorynchus mykiss) feeding

Olive mill vegetation water (VW) is an olive oil by-product rich in polyphenols has powerful antioxidant effects. In light of the interest on the research of novel natural antioxidants to use in fish feed, the aim of this research was to use VW as a potential substitute for artificial antioxidants in rainbow trout diet as well as checking its effects on the blood chemistry and digestive organ physiology of the fish. The experimental plan was monofactorial, balanced (4 × 3) and the experimental factor considered was the fish diet. Diets were isoproteic (CP 40%) and isoenergetic (18 MJ kg⁻¹ DM) with two inclusion levels of VW (1 and 5%: VW1 and VW5) tested against a control diet. A feeding trial was performed on quadruplicate groups of 200 fish (mean body weight: 44.2 g) fed experimental diets for 94 days. At the end of the trial, the growth performance traits were determined and sampling of blood and different tissues (brain, ovary, stomach, liver, and intestine) were carried out for haematology, endocrinology, histology, and digestive enzyme analysis. The main results of the present experimentation are that VW inclusion in rainbow trout feed slightly affects the productive traits and blood chemistry, while the histological structure of digestive organs and digestive enzyme physiology were not affected.