Zebrafish are increasingly used in biomedical research but their welfare needs are often given less consideration than mammalian research subjects.
The exclusion of zebrafish larvae from welfare protection based on developmental stage ignores evidence that larval fish respond to noxious stimuli in ways consistent with pain experience. Larvae and adults in overcrowded or poor-quality water conditions show elevated stress responses. As their use in research grows, welfare standards for zebrafish need urgent development to match standards applied to mammalian subjects.