Effects of Olive Leaf (Olea europaea) Phenolic Extract on Zootechnical Parameters, Centesimal Composition, and Biochemical Parameters of Nile Tilapia (Oreochromis niloticus) Juveniles.

This study evaluated the effects of dietary olive leaf extract (OLE) on Nile tilapia (Oreochromis niloticus) juveniles, focusing on growth parameters, centesimal composition, biochemical responses, and lipid peroxidation. OLE was extracted with 60% ethanol (1:20 w/v). Five diets, containing 34% crude protein and 8% lipids, were tested: a control (0 g/kg) and four with increasing OLE levels (0.25, 0.5, 1, and 2 g/kg). The 46-day trial included 225 fish (0.56 ± 0.11 g) distributed in 15 tanks. Growth performance was not affected, except for a higher condition factor in OLE0.25. This dose also resulted in lower moisture and higher lipid content, while all OLE treatments increased crude protein in fish. Muscle glycogen decreased in all OLE-fed groups, and liver glycogen was reduced in OLE0.25. Plasma triglycerides decreased in OLE0.5 and OLE0.25, while total plasma protein was lower in OLE2.0. Liver triglycerides were lower in OLE0.25 and higher in OLE0.5, whereas glucose showed a glycemic peak in OLE2.0. Hepatic lipid peroxidation was reduced in OLE2.0. Overall, dietary OLE did not compromise the growth performance of Nile tilapia, and 0.25 g/kg promoted beneficial effects on centesimal composition, biochemical parameters, and lipid peroxidation, highlighting its potential as a functional ingredient in aquafeeds.