Zebrafish have become the third most commonly used vertebrate in biomedical research globally, yet welfare standards for their housing, handling and experimental procedures lag significantly behind those for mammals, partly due to assumptions about their limited sentience.
Welfare assumptions about zebrafish in research settings are often based on outdated views of fish cognition that have been substantially revised by evidence of pain behaviour, fear responses and social complexity. Standard housing in bare tanks without refuge, substrate or environmental complexity prevents expression of natural behaviour. Water quality problems — common in large-scale zebrafish facilities — cause chronic physiological stress. Experimental procedures are frequently performed without analgesia on the assumption that fish do not experience pain, despite evidence to the contrary. The rapid growth of zebrafish use in research makes improving welfare standards for this species a high-priority intervention given the numbers affected.