Unlocking the potential of nutmeg oil: A sustainable alternative for rainbow trout anesthesia in aquaculture

In aquaculture, interest in natural anesthetic agents as alternatives to synthetic anesthetics has been steadily increasing. This is due to concerns over residue accumulation, environmental impact, and growing demand for sustainable practices. Within this context, the present study focused on the anesthetic effects of nutmeg essential oil at three different concentrations in rainbow trout ( Oncorhynchus mykiss , 94.42 ± 23.9 g): low (400 µL/L), medium (600 µL/L), and high (800 µL/L). Induction and recovery times were recorded, and samples were collected at 0, 2, 4, and 8 hours post-anesthesia for antioxidant, cortisol, and hematological analyses. Additionally, gill tissues were sampled immediately after anesthesia for histological examination. While the induction time for the low concentration exceeded 3 minutes, the induction and recovery times for the other concentrations ranged within acceptable limits (3 min for induction and 5 min for recovery). Blood parameters exhibited an increasing trend until the 4th hour post-anesthesia, peaking at the 2nd hour, before returning to control levels by the 4th hour. Histological evaluation revealed healthy gill tissues in the control and low-concentration group (400 µL/L), whereas hyperplasia was observed in the medium (600 µL/L) and high-concentration (800 µL/L) groups. Antioxidant enzyme activity (superoxide dismutase (SOD), catalase (CAT), malondialdehyde (MDA), and glutathione peroxidase (GSH-Px)) indicated potential oxidative stress at the high anesthetic concentration. Similarly, cortisol levels were higher at the high concentration, with plasma cortisol showing a slight initial increase followed by a return to normal levels over time. In conclusion, this study highlights that nutmeg oil at a concentration of 600 µL/L may serve as a promising natural alternative to synthetic anesthetics in aquaculture. However, future studies should include a synthetic anesthetic as a control to allow for direct comparisons and a more comprehensive evaluation of its efficacy and physiological effects. • Medium (600 µL/L) and high (800 µL/L) doses showed acceptable induction and recovery times. • Gill tissues were healthy in low-dose (400 µL/L) and control groups; hyperplasia in others. • High doses (800 µL/L) caused oxidative stress, shown by antioxidant enzyme activity. • Nutmeg oil at 600 µL/L is a viable alternative to synthetic anesthetics.