Zebrafish are used in millions of research procedures annually, but welfare standards lag far behind those for mammals. Improving zebrafish husbandry and experimental design is a major welfare opportunity.
Zebrafish have become the vertebrate model of choice for many research fields, but their welfare has not kept pace with their scientific centrality. High stocking densities cause stress and aggression; suboptimal water quality causes chronic physiological strain; and the welfare implications of genetic modifications are rarely assessed prospectively. Improving zebrafish welfare requires facility-level changes in husbandry standards, researcher training in pain recognition and anesthesia use, and prospective welfare review of transgenic and mutant lines for phenotypes causing ongoing distress.