Zebrafish are used in millions of research procedures annually and have gained increasing regulatory protection. Their welfare needs and the ethical framework for their use in research are evolving rapidly.
Zebrafish welfare has been relatively neglected compared to mammalian research animals, partly because their aquatic nature makes welfare assessment less intuitive for researchers trained with mammals. The extension of regulatory protection to fish in EU research has begun to shift this, requiring project license applications to address zebrafish welfare formally. Key welfare concerns include crowding that elevates cortisol chronically, inadequate environmental enrichment, inappropriate water quality, and handling stress during routine procedures. The 3Rs framework applied rigorously to zebrafish research — seeking replacement alternatives where possible, minimizing numbers used, and refining procedures to reduce suffering — represents genuine ethical progress in one of science's most widely used model systems.