Zebrafish are used in millions of experiments annually. Their welfare requirements are well-defined but not always met. Understanding zebrafish welfare improves research and reduces suffering.
Zebrafish welfare was historically neglected relative to rodents because of their small size and aquatic nature. However, robust evidence shows they experience stress, pain and social deprivation. The 3Rs framework applies fully: replacement with organoid or in vitro systems where possible, reduction in numbers through improved experimental design, and refinement of housing and husbandry to minimise suffering. Social housing in appropriate-sized groups, environmental enrichment with objects and substrate, and humane endpoint selection all reduce welfare costs without compromising scientific validity.