Zebrafish are the most widely used fish in biomedical research, with growing recognition that their welfare matters and that improved welfare practices benefit both the fish and the quality of research outcomes.
Zebrafish welfare has historically received less attention than mammalian research species, but their widespread use and evidence of sentience argues for meaningful welfare standards. Social isolation from conspecifics causes measurable stress. Inadequate environmental conditions including inappropriate temperature, water quality, and light cycles affect both welfare and experimental reproducibility. The transition from larvae (currently unregulated) to juveniles (regulated) represents a regulatory gap that the welfare evidence suggests should be revisited. Improving zebrafish welfare benefits both the fish and the scientific outcomes.