Methods of humane killing of laboratory fish: FELASA Working Group recommendations (2025)

Mocho, J.-P., Blasco, J. R., Lundegaard, P. R. et al.

Abstract

As commissioned by the Federation of European Laboratory Animal Science Associations, these working group recommendations define the requirements to achieve the humane killing of fish, compare methods of killing, recommend methods of killing depending on context, and detail protocols leading to good practice. With a review of current practices in a fish laboratory and available literature to guide the recommendations, the concept of ideal euthanasia is discussed, and the dilemma of a prompt but stressful death versus a slow but stress-free experience is introduced. Noticeably, the context of fish killing varies widely whether to satisfy European Directive requirements, efficacy for species and/or developmental stages, scientific needs, health and safety, or animal welfare. Examples in the recommendations are based on the most common laboratory fish species, such as zebrafish Danio rerio, and the most commonly used methods of killing, such as overdose of anaesthesia, hypothermic shock, electrical stunning, and concussion – percussive blow to the head. Practical applications of completion of death, refinements, and protocols for good practice are proposed for all developmental stages and depending on the potential fate of the carcass as a scientific sample.