Zebrafish have become one of the most widely used vertebrate research models, yet welfare standards lag significantly behind those for mammals, and their capacity to experience pain and stress is increasingly supported by evidence.
Zebrafish welfare in research is a rapidly evolving area. Early assumptions that fish welfare was less important than mammalian welfare are being challenged by accumulating evidence that zebrafish experience pain, stress, and fear in ways that warrant meaningful ethical consideration. Standard housing — small tanks, continuous lighting, sparse environments — violates their natural shoaling, foraging, and diurnal behavior patterns. The use of zebrafish larvae below the regulated welfare threshold (typically 5 days post-fertilization in many jurisdictions) raises questions about when sentience develops and where protections should begin. Refinements including social housing, environmental enrichment with plants and substrate, appropriate lighting cycles, and pain management during procedures can meaningfully reduce suffering with minimal impact on research outcomes.