Zebrafish are the second most commonly used vertebrate in biomedical research, with growing evidence of their pain sensitivity and complex behavior raising welfare questions about research practices and housing standards.
Zebrafish occupy an awkward position in animal welfare consideration - widely used in research precisely because they are perceived as simpler than mammals, yet demonstrating behavioral and physiological responses that indicate genuine welfare relevance. The 3Rs framework (Replacement, Reduction, Refinement) applies to zebrafish but has historically been applied less rigorously than for rats and mice. Refinement opportunities include environmental enrichment, social housing protocols, appropriate analgesia, and humane endpoints that minimize suffering duration. As zebrafish research expands, welfare science must keep pace to ensure proportionate protection for animals whose sentience is increasingly established.