LAUSR

Abstract This study tested the use of essential oil of Ocimum gratissimum (EOOG) as an anesthetic for juvenile Lophiosilurus alexandri and its efficiency in mitigating the effects of handling stress. Two experiments were performed. Experiment 1 determined the time for anesthesia induction and recovery and the ventilatory frequency of juveniles exposed to different concentrations of EOOG (0, 10, 30, 90, 150 and 300 mg L−1). Based on the results of Experiment 1, Experiment 2 evaluated the effects of 0, 10 and 90 mg L−1 of EOOG on blood parameters and oxidative stress in liver and brain immediately after induction and one hour after recovery. No mortality was observed in any experiment. In Experiment 1, times for anesthesia induction were shorter, and recovery times longer, with increased EOOG concentrations. Compared to the animals anesthetized with 0, 10 and 30 mg L−1 of EOOG, higher ventilatory frequencies were observed during induction for animals anesthetized with 90, 150 and 300 mg L−1. In experiment 2, variations on hematological variables derived from EOOG exposition were determined, but parameters returned to baseline levels one hour after recovery. The use of 90 mg L−1 EOOG prevented increased plasma glucose and cortisol levels one hour after handling. However, animals anesthetized with 90 mg L−1 EOOG had higher concentrations of ROS (hepatic and brain) after induction and one hour after recovery. The increase in ROS for animals anesthetized with 90 mg L−1 was not matched by the antioxidant defense system, which showed a reduction in brain GST activity one hour after recovery. Juveniles anesthetized with 10 mg L−1 EOOG only presented an increase in hepatic ROS one hour after recovery from anesthesia, however, there was a response from the antioxidant defense system, with an increase in brain and hepatic GST. The increase in ROS in treatments submitted to handling under the effect of anesthesia did not cause tissue damage. It is concluded that the use of 90 and 150 mg L−1 EOOG cause anesthesia in L. alexandri within the ideal intervals of induction and recovery. The use of 90 mg L−1 EOOG prevented higher levels of plasma glucose and cortisol one hour after handling, and induced changes to the antioxidant defense system, increasing the concentration of liver and brain ROS, and reducing the activity of brain GST one hour after recovery.