Zebrafish and other fish species are increasingly used in biomedical research, raising welfare questions about their status as research subjects and the application of 3Rs principles to aquatic species.
Laboratory fish welfare has developed substantially slower than mammalian research welfare because fish have historically received less moral consideration, and because the scientific community has been slower to apply the 3Rs to aquatic species. Yet zebrafish and other research fish have demonstrated pain responses, stress behaviors, and cortisol responses to adverse conditions that are consistent with welfare-relevant experience. The millions of fish used annually in biomedical research deserve the same 3Rs consideration applied to mammals: replacement where alternatives exist, reduction in numbers where possible, and refinement of procedures and housing to minimize suffering. The development of validated welfare indicators, appropriate anesthetic protocols, and enriched housing designs for research fish is advancing, but implementation in research facilities remains uneven.