Zebrafish are the second most used vertebrate in biomedical research after mice. Their welfare needs are increasingly recognized as they gain regulatory protections in the EU and other jurisdictions.
Zebrafish welfare is an area where regulatory protection has rapidly expanded following scientific recognition of their capacity for suffering. Key welfare concerns include: social isolation (zebrafish are shoaling fish that suffer in isolation), inadequate environmental complexity, inappropriate water temperature and quality, and the use of inhumane methods for tissue harvesting or euthanasia. The 3Rs framework (Replacement, Reduction, Refinement) applies fully to zebrafish research. Refinements include group housing, environmental enrichment, appropriate anesthesia, and humane endpoints. The question of larval zebrafish welfare — before they begin feeding — is an active scientific and regulatory debate.