Zebrafish are the second most commonly used vertebrate in biomedical research globally, yet welfare standards lag far behind those for mammals. Their sentience and welfare needs are increasingly recognized.
Zebrafish welfare in research exemplifies the challenge of applying welfare standards to aquatic species used at very large scale. The sheer number of animals involved means even small improvements in per-animal welfare conditions translate to enormous aggregate welfare benefit. Key welfare issues include water quality, stocking density, social housing, light cycles, and enrichment provision. The larval exclusion from legal protection in many countries is increasingly questioned as neuroscience evidence documents pain-related responses earlier in development. Refinement of experimental protocols to reduce handling stress and improve housing conditions is an active area of research.