Zebrafish have become a major biomedical research model, and their welfare deserves the same attention as rodents despite common assumptions that small fish matter less.
Zebrafish welfare has historically received less attention than rodent welfare partly due to assumptions that small fish are simpler or feel less. The regulatory gap — larvae under 5 days not protected in the EU — means the majority of zebrafish experiments occur outside welfare oversight. Evidence shows adult zebrafish experience stress, show conditioned avoidance of painful stimuli and benefit from social housing and environmental enrichment. Water quality management is the most critical welfare determinant in zebrafish facilities: ammonia and temperature fluctuations cause chronic physiological stress that affects both welfare and research validity. Improving zebrafish welfare standards is both an ethical obligation and a scientific quality issue.