Evaluation of different concentrations of eugenol (Syzigium Aromaticum) on electrocardiography of Nile tilapia (Oreochromis niloticus) .(Linnaeus 1758)

The present study evaluated the effects of increasing concentrations of eugenol on cardiac electrophysiological activity in Oreochromis niloticus (Nile tilapia) to establish a humane and effective euthanasia protocol. Forty-five fish (24.38 ± 2.5 g) were randomly assigned to five groups: control, vehicle (70% ethanol), and three eugenol treatments (700, 800, and 900 µL L⁻¹). Electrocardiographic (ECG) recordings were obtained using silver electrodes and a high-impedance amplifier for 30 minutes. Cardiac parameters, including heart rate, QRS amplitude, and PQ, RR, and QT intervals, were analyzed using ANOVA and Tukey’s tests. A concentration-dependent decrease in heart rate and ECG amplitude was observed. The 700 µL L⁻¹ group showed a 53.8% reduction in heart rate compared with the control, whereas 800 µL L⁻¹ and 900 µL L⁻¹ induced complete cardiac arrest within 30 minutes of exposure. These results demonstrate that eugenol exerts a dose-dependent depressive effect on cardiac excitability in O. niloticus , supporting its use as a humane euthanasia agent for experimental and aquaculture settings. The findings provide electrophysiological evidence of cardiac inhibition induced by high eugenol concentrations, contributing to the refinement of fish welfare protocols.