Zebrafish are increasingly used in biomedical research but their welfare needs are often inadequately addressed. Understanding zebrafish cognition and pain capacity informs better standards for their care and use.
Zebrafish welfare is a rapidly evolving area at the intersection of welfare science and regulatory policy. The massive scale of zebrafish use in research — and the regulatory gap that excludes larval zebrafish from animal welfare protections — creates a situation where billions of small fish with documented nociceptive systems may be subjected to procedures without the welfare protections applied to mammalian research subjects. The scientific case for extending welfare consideration to zebrafish at developmental stages beyond current regulatory thresholds is growing: their nociceptive systems are functional at stages earlier than regulation typically requires, and their behavioral responses to noxious stimuli — avoidance, rubbing injured areas, altered locomotion — are consistent with pain experience. Social housing requirements reflect another welfare dimension: zebrafish are naturally shoaling animals whose isolation causes stress indicators measurable through cortisol and behavior. Enriched tank environments including substrate, plants, and shelters significantly improve zebrafish behavioral indicators of welfare. The 3Rs framework applied to zebrafish research is a developing field with meaningful room for welfare improvement in facilities that have not yet adopted best practice social housing and enrichment standards.