Zebrafish are increasingly used in biomedical research, raising welfare questions about their needs and appropriate housing standards.
Zebrafish welfare has historically received less attention than mammalian research models despite their vertebrate status and evidence of pain responsiveness. Housing in densely stocked, barren tanks without environmental complexity causes chronic stress measurable through cortisol levels and immune markers. Social isolation causes behavioral changes consistent with distress. The 3Rs principles (Replace, Reduce, Refine) apply to zebrafish as they do to other vertebrates, but implementation has lagged behind mammalian model standards. As zebrafish use continues to expand, establishing and enforcing appropriate welfare standards is increasingly urgent.