Group housing of zebrafish in research settings significantly improves welfare compared to isolation, with minimal impact on most experimental outcomes.
Zebrafish social welfare is a well-documented welfare dimension that is often inadequately addressed in research settings for practical or experimental reasons. The stress of isolation in a social shoaling species is not trivial — it produces physiological changes that can confound experimental results while simultaneously causing welfare harm. The solution — group housing — often improves experimental validity alongside welfare outcomes. Research designs that require isolated zebrafish for experimental reasons should treat isolation as an experimental intervention in itself, minimizing isolation duration, providing visual or olfactory contact with conspecifics where possible, and using adequate sample sizes to account for isolation stress as a variable.