Zebrafish are widely used in biomedical research and increasingly in aquaculture. Their welfare needs are often overlooked despite evidence of sentience and pain capacity.
Zebrafish have historically been treated as low-welfare vertebrates due to their small size and assumed simplicity. However, accumulating evidence shows they possess nociceptors, endogenous opioid systems, and behavioral responses consistent with pain experience. Group housing is important for their social needs, and environmental complexity improves welfare indicators. As their use in research scales up, systematic welfare standards are urgently needed.