Zebrafish have become one of the most widely used vertebrate model organisms in biomedical research, but welfare standards for these small fish have lagged behind those for mammals despite growing evidence of their sentience and capacity for suffering.
Zebrafish welfare has historically received less attention than mammalian laboratory animal welfare, partly because their small size and aquatic nature made them seem less welfare-relevant. Evidence of zebrafish sentience has accumulated substantially: they show pain-indicative behaviours reversed by analgesics, display stress responses to social isolation, learn to avoid noxious stimuli, and demonstrate individual variation in anxiety-like responses. Standard laboratory housing in sparse tanks without social groups or environmental enrichment fails to meet these demonstrated needs. Simple enrichment including artificial plants, substrate, and appropriate shoal groupings reduces stress indicators without compromising experimental outcomes. Regulatory frameworks for zebrafish welfare are improving but still lag behind those for mammals.