Effects of thymol and carvacrol anesthesia on the electrocardiographic and behavioral responses of the doctor fish Garra rufa

Abstract

The present study examined the anesthetic efficiency and electrocardiographic and behavioral responses of the doctor fish Garra rufa anesthetized with thymol and carvacrol. Fish were subjected to anesthetic baths in five different concentrations of the thymol (25, 50, 75, 100, and 150 mg L−1) and carvacrol (25, 50, 75, 100, and 150 μL L−1). Induction and recovery times were recorded for each fish separately, and 10 fish were used per anesthetic concentration. Video tracking and processing were performed for each anesthetic to obtain changes in behavioral parameters between anesthetic concentrations. Thereafter, a different experiment was established for cardiographic evaluations, and necessary electrocardiographic (ECG) records were obtained in 5 fish. At the end of the experiments, all tested thymol and carvacrol concentrations effectively induced anesthesia in G. rufa. Video tracking analyses demonstrated that G. rufa did not exhibit any changes in behavioral parameters when submitted to 25–50 mg L−1 concentrations of thymol compared to anesthetic-free water. However, movement distance and mobility significantly increased with increasing carvacrol concentrations. We found that high concentrations of thymol (150 mg L−1) and carvacrol (100 and 150 μL L−1) caused avoidance behaviors in G. rufa. ECG recordings showed that heart rate decreased, and PR and QT intervals were prolonged with increased thymol concentrations. Thymol concentrations did not affect PQ intervals. No significant changes in ECG parameters were observed with carvacrol. These results demonstrated that concentrations of 25 and 50 mg L−1 thymol and 50 μL L−1 carvacrol can be used for general aquaculture procedures, and 100 mg L−1 thymol and 75 μL L−1 carvacrol can be used as rapid anesthesia in G. rufa.