Zebrafish have become one of the most important model organisms in biomedical research, with welfare considerations increasingly important as their use grows to tens of millions annually.
Zebrafish welfare in research facilities deserves more attention as their numbers have grown enormously. Crowded housing reduces normal shoaling behavior and increases aggression. Temperature and water chemistry are critical for their welfare and health. Procedures including fin clipping, microinjection, and behavioral testing cause pain and stress. Euthanasia methods including MS-222 overdose and ice water immersion have different welfare properties. Larvae under 5 days post-fertilization are often not counted in animal use statistics, creating a potential welfare blind spot as experiments frequently target early development stages. Their transparency and external development make them valuable for welfare-reduced alternatives to mammalian models in some applications.