Laboratory fish, particularly zebrafish and medaka, are used in enormous numbers in biomedical research, and welfare refinement strategies are reducing suffering while maintaining scientific validity.
Laboratory zebrafish welfare has historically received far less attention than that of mammals in research settings, creating a significant welfare gap given the enormous numbers used. Zebrafish are regulated in many countries as research animals only from a certain developmental stage, leaving larval welfare in a regulatory gray area despite evidence of early pain-like responses. Refinement strategies including environmental enrichment, appropriate analgesia for painful procedures, and optimized handling protocols can substantially reduce welfare burden without compromising scientific validity. Indeed, animals in better welfare conditions often produce more reliable experimental data due to reduced stress-related variability. The scale of potential welfare improvement from systematic refinement in zebrafish research is vast given the numbers involved.