Current research and guidelines for euthanasia in laboratory fish with a focus on fathead minnows

This paper reviews the methods and approaches used to humanely anesthetize (render unconscious) and or euthanize (kill) laboratory fish (in research settings), with a specific focus on the fathead minnow. We surveyed the literature (333 scientific studies published 2004-2021) to examine euthanasia methods used for various life stages. Our findings showed that many published scientific papers do not provide an adequate description of anesthesia or euthanasia methods, particularly for larval fathead minnows. Over the two decades there was a 20% increase in the number of papers that described their euthanasia method(s). In addition, the review shows evidence that younger minnows require higher concentrations of anesthetic (compared with adults) for effective euthanasia. Recommendations from the review include the use of a two-step euthanasia method (immersion in anesthetic followed by spinal severance and/or exsanguination). As well, it is recommended that details of anesthesia and euthanasia are more fully captured in published scientific manuscripts to allow for comparison among studies and for progress in animal welfare methods. Specific research questions remain on whether rapid cooling is a humane first-step euthanasia method, better investigations into understanding when anesthesia has occurred in fish, and research into methods of euthanasia in larval and juvenile fish.