Zebrafish have become one of the most widely used vertebrates in biomedical research, with growing evidence they are sentient and deserve welfare consideration.
Zebrafish welfare has been largely overlooked because their small size and aquatic nature make suffering less visible. Evidence of pain responses and cognitive capabilities argues for applying the 3Rs principle to zebrafish research. Larval stages below 5 days post-fertilization often lack welfare protection in law despite developing nervous systems.