Zebrafish are increasingly used in biomedical research as an alternative to rodents, but their welfare needs are frequently underestimated due to their non-mammalian status.
Zebrafish welfare has historically received less attention than mammalian research species due to assumptions about their lesser sentience. However, zebrafish display behavioral and physiological stress responses, learn from experience, and show social bonding. Poor water quality causes physiological stress equivalent to toxic exposure. Overcrowded tanks produce aggressive interactions and resource competition. The scale of zebrafish use — with facilities housing tens of thousands of fish — means that small welfare improvements per animal translate to large aggregate benefits. Applying the same rigor to zebrafish welfare assessment as to rodent welfare would significantly reduce preventable suffering across this growing research population.