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

## TL;DR

Adding olive leaf extract to the diet of Nile tilapia juveniles improved their body composition and health without affecting growth, suggesting it could be a natural alternative to synthetic additives in aquaculture.

## Contribution

The study demonstrates that low-dose olive leaf extract can enhance fish health and sustainability in aquaculture.

## Key findings

- Olive leaf extract at 0.25 g/kg improved body composition and reduced liver fat oxidation in Nile tilapia.
- Fish growth was unaffected, but biochemical parameters like plasma triglycerides and liver lipid peroxidation were positively influenced.
- Higher doses of extract had mixed effects, with some parameters showing adverse changes.

## Abstract

Fish farming plays a key role in producing healthy food and meeting the growing demand for animal protein. However, producers face challenges in maintaining fish health while reducing the use of synthetic additives. Olive leaves, a by-product of olive oil production, are rich in natural compounds that may improve fish health and product quality. In this study, we tested whether adding small amounts of olive leaf extract to the diet of Nile tilapia juveniles could improve their growth, body composition, and health indicators. The fish were fed for 46 days with diets containing different amounts of olive leaf extract. Fish growth was not affected, but the lowest amount tested improved the proportion of healthy nutrients in the fish’s body, balanced certain blood parameters, and reduced fat oxidation in the liver, which is linked to better health. These results suggest that olive leaf extract can be used as a natural feed additive to promote fish health and make aquaculture more sustainable, while also adding value to an agricultural by-product that would otherwise be discarded.

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.