Zebrafish have become the second most widely used vertebrate in biomedical research, making their welfare increasingly significant as evidence for fish sentience grows.
Zebrafish welfare in research sits at the intersection of the expanding evidence for fish sentience and the rapid growth of their use in biomedical science. Their regulatory status as vertebrates in most jurisdictions means the 3Rs framework applies, but implementation has lagged behind that for mammals. Overcrowded housing, inadequate environmental enrichment, and absent analgesia for painful procedures are documented welfare issues at facilities globally. The welfare science specific to zebrafish is advancing, providing practical guidance for housing, environmental enrichment, and humane endpoint criteria that can meaningfully reduce suffering in this growing research population.