Refinement of welfare for zebrafish and medaka in biomedical research addresses the growing use of these species and the welfare obligations that accompany their increasing regulatory recognition.
Laboratory fish welfare has historically been considered only minimally, on the assumption that fish sentience is limited. Accumulating evidence of fish nociception and stress physiology has shifted regulatory and ethical frameworks substantially. The three Rs — replacement, reduction, refinement — now apply to zebrafish with meaningful enforcement in the EU and increasingly elsewhere. Refinement advances including optimized group housing, enriched tank environments, and refined anesthesia protocols are demonstrating that welfare-improved zebrafish research produces more reliable and reproducible results, creating a scientific as well as ethical case for implementation.