Behavioural and physiological effects of methadone in the perioperative period on the Nile tilapia Oreochromis niloticus

: Through the analysis of behavioural changes, this study demonstrates that methadone has behavioural, but not analgesic, effects on Oreochromis niloticus. It provides information that suggests the drug has sedative abilities, as the recovery time was shorter in the fish receiving methadone. Future research, with different doses and stimuli, is required to provide more information about analgesia.