This work tested the effectiveness of menthol as anesthetic for Nile tilápia (Oreochromis niloticus) by the evaluation of behavioral events, the safety margin of the anesthetic, and stress response. On first experiment, six different anesthetic concentrations were tested to evaluate the induction time to anesthesia. On second experiment, two tests were carried out to verify the safety margin of the anesthetic. On third experiment, stress responses were evaluated. The safe concentration to induce a surgical anesthesia was 250mg L-1. To a brief handling and visual inspection, the appropriated concentration was 150-200mg L-1. There was no mortality after exposure to 500mg L-1, indicating a good safety margin for this anesthetic. Menthol even in its adequate dosage induced a rise in glucose concentrations indicating a stress response of the fish. Thus menthol is an ineffective anesthetic to juveniles tilapia during routine procedures in fish culture.
fish; Oreochromis niloticus; stress; sedation
