Zebrafish are among the most widely used vertebrates in biomedical research. Growing evidence of their capacity for pain and stress motivates welfare improvements in laboratory housing.
Zebrafish have historically been treated as low-welfare organisms in research due to their small size and perceived simplicity, but evidence accumulating over the past decade indicates they experience stress, pain, and social deprivation in ways that matter morally. Standard barren research tanks deny zebrafish their natural behaviors of schooling, foraging, shelter-seeking, and substrate interaction. Enriched housing with plants, substrate, and shelter reduces cortisol levels and stereotypic swimming patterns. The 3Rs principle (Replace, Reduce, Refine) applies fully to zebrafish, and refinement opportunities through housing improvements, social housing, and analgesia for painful procedures are significant. Regulatory frameworks in many jurisdictions now require welfare consideration for zebrafish, but implementation in practice varies widely.