Zebrafish are increasingly used in biomedical research due to their genetic tractability and optical transparency, and their welfare needs deserve attention as their use continues to grow rapidly.
Zebrafish represent the growing edge of vertebrate welfare consideration in research. Their use has expanded rapidly because they combine genetic amenability with lower perceived welfare costs than mammals — but this perception requires scrutiny. Zebrafish demonstrate pain responses, stress physiology, and social behavioral needs that parallel those of other vertebrates. Welfare standards for zebrafish are less developed than for rodents, creating risk of inadequate housing, monitoring, and anesthesia practices. The extension of EU regulatory protections to zebrafish larvae was a significant step, but implementation and enforcement remains inconsistent. As numbers of zebrafish used in research grow into the hundreds of millions annually, the welfare implications of suboptimal care become substantial even if individual fish welfare costs are modest.