Zebrafish are the most widely used vertebrate in biomedical research after mice and rats, but their welfare needs have historically been underserved due to assumptions about fish sentience and regulatory gaps.
Zebrafish welfare has been systematically undervalued because of historical assumptions that fish do not experience pain or have welfare needs worth addressing. The evidence that zebrafish nociception is functionally analogous to that of mammals, and that analgesics reduce their protective responses to noxious stimuli, has shifted scientific consensus toward taking zebrafish welfare seriously. Isolation of highly social schooling fish causes measurable stress; experiments that require individual housing impose welfare costs that should be minimised and justified. Barren tanks prevent the environmental exploration and social interaction that zebrafish engage in naturally. Early developmental stages (larvae and embryos) are used extensively and their welfare status is under active scientific investigation. The 3Rs framework — replacement, reduction, refinement — applies to zebrafish as to other vertebrates, but its implementation in zebrafish research has lagged behind mammalian species.