Fish are used in enormous numbers in research, often with less welfare oversight than mammals. Extending the 3Rs framework to fish is an ongoing welfare improvement effort.
Fish welfare in research represents a significant welfare gap between scientific knowledge and regulatory practice. The evidence for fish pain and sentience is now robust enough to inform welfare obligations, yet many research contexts continue to use fish without the same welfare scrutiny applied to mammals. The 3Rs framework applies to fish in EU research but implementation varies significantly. Analgesia for painful fish procedures is the most immediate welfare improvement available - the evidence that fish experience pain sufficient to require pain relief is strong, but application in research contexts is inconsistent. Housing improvements that allow schooling behavior and species-appropriate social grouping represent the next tier of welfare improvement.