*2.3. Animals*

In total, 50 adult (sex ratio was about 50:50 male:female, 3–4-month old, and 3–4 cm in length), wild-type short-fin strain zebrafish (*Danio rerio*) purchased from an authorized commercial dealer (Pet Product S.R.L., Bucharest, Romania) were used in the present study and acclimated for at least two weeks before experiments. Fish were fed twice daily with Norwin Norvitall flake (Norwin, Gadstrup, Denmark). Animals were randomly divided into groups of 10 fish/24 L housing tanks filled with unchlorinated water under a 14 h/10 h light/dark cycle. The water within the tanks was constantly aerated (7.20 mg O2/L) using Tetra*tec*® air pumps (Tetra, Melle, Germany) and filtrated to avoid the accumulation of organic toxins. The water parameters were kept in the following ranges: pH 7.5, conductivity 500 μS, ammonium concentration < 0.004 ppm, and temperature 26 ± 1 ◦C. For the behavior studies, acclimated zebrafish were randomly assigned into the control, the scopolamine (Sco, 100 μM, Sigma-Aldrich, Darmstadt, Germany), and three REO treatment groups (25, 150, and 300 μL/L). The doses of the essential oil were chosen with reference to previous reports [24]. REO (25, 150, and 300 μL/L) was administered individually by immersion to zebrafish (*Danio rerio*) through transferring into 500 mL glass for 1 h, once daily for eight days, whereas scopolamine (100 μM) treatment was delivered individually by transferring into a 500 mL glass, 30 min before behavioral tests. The control group was immersed only in unchlorinated water. The working protocol (as summarized in Figure 1) was approved by the local board of ethics for animal experimentation (No. 15309/2019) and fully complied with the Directive 2010/63/EU of the European Parliament and of the Council of 22 September 2010 on the protection of animals. Efforts were made to reduce animal suffering and the number of animals utilized.

**Figure 1.** Scheme of the working protocol.
