Zebrafish are increasingly used in biomedical research, and their welfare requirements including appropriate social housing, water quality, and enrichment are often inadequately provided.
Zebrafish welfare is an area where the rapid growth of their use in research has outpaced the development of welfare standards and husbandry knowledge. As social shoaling fish, isolated or small-group housing causes demonstrable stress that affects both welfare and experimental outcomes. Enrichment approaches including shoal companions, substrates, and tank complexity reduce stress indicators and improve welfare without compromising research validity. The evidence that zebrafish experience pain-like states and engage in avoidance learning strengthens the welfare case for applying the 3Rs rigorously. The 3Rs guidance for zebrafish specifically — including group housing requirements, minimum water quality standards, and refinement of sampling and euthanasia procedures — is available but inconsistently implemented.