Many people have asked me what is the best method for “putting fish to sleep”. As veterinarians, we have access to anaesthetics.
But for the general public this will not be the case. Members of the public may be able to access clove oil from their local pharmacy or chemist. The active ingredient is eugenol. Being an oily liquid, this will need to be pre-dissolved by shaking several drops of the oil in a bottle of water. This solution can then be added to the aquarium that is holding the fish to be euthanased. The final dose rate is approximately more than 10 drops per litre of water.
A fish’s heart will continue to beat for a relatively long time, and so, your fish will need to remain in this solution for an additional of at least 30 minutes after signs of last opercular movements, to ensure the anaesthetic has resulted in death. A secondary method of euthanasia may be used, provided your fish is fully anaesthetised (and cannot feel pain).
Leaving fish in the aquarium to die slowly without medical attention is inhumane.