Zebrafish are increasingly used in pain research, with their welfare during studies raising important questions about the ethics of using one sentient species to study pain for another.
Zebrafish pain research presents an acute ethical paradox: the suffering we study in these animals to understand pain and develop analgesics for other species is directly borne by the research subjects. A zebrafish in a formalin injection pain model is experiencing what the model is designed to measure - genuine pain-like experience. The ethical weight of this depends on the degree of sentience we ascribe to zebrafish, which is contested but increasingly supported. The most welfare-positive approach to zebrafish pain research includes minimizing study duration, using effective humane endpoints, seeking pain studies that measure effects of already-characterized pain rather than inducing novel pain, and actively supporting alternative model development.