Fish used in biomedical research are covered by legal welfare protections in many jurisdictions, but their pain capacity is often underestimated and their welfare needs are frequently inadequately met.
Fish welfare in laboratory settings suffers from a combination of outdated assumptions about fish sentience and regulatory gaps that leave fish without legal protection in some jurisdictions. The neurological evidence that fish experience pain and fear has accumulated substantially, but this knowledge has not translated quickly into practice. Fish kept in barren, overcrowded tanks experience chronic stress reflected in abnormal behaviour and elevated cortisol. Anaesthetic overdoses are common when researchers lack training in fish physiology. Procedures performed without anaesthesia on the assumption that fish do not feel pain are increasingly recognised as ethically unjustifiable. Welfare improvements including enriched housing, social grouping, optimised anaesthetic protocols, and earlier humane endpoints would reduce suffering without compromising scientific validity.