Zebrafish are the second most commonly used vertebrate in research. Though often perceived as low-welfare organisms, evidence suggests they experience pain and stress warranting formal welfare consideration.
The welfare status of zebrafish has historically been underestimated due to their small size and perceived simplicity. Evidence of nociception, stress responses, and learned avoidance behavior argues for taking their welfare seriously. Housing improvements including appropriate group sizes, tank complexity, and water quality monitoring can substantially reduce chronic stress in these animals.