Euthanasia for pet fish

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Euthanasia for pet fish

December 06, 2017 - 08:51

The text below is the recommendation of Fish Veterinarian Richmond Loh of Australia, and is suitable for all fish - both Koi and aquarium species.  Please read the notes after the article...

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 (or bowl) that is holding the fish to be euthanased. The final dose rate is approximately more than 10 drops per litre of water. (see note below)

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 (gill) 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 (or pond) to die slowly without medical attention is inhumane.

K.O.I. would like to add that for large Koi, you will need a dose that is 4-10 times the amount above (Roberts, 2010), and it is much easier to dissolve in vodka than water. The scent of clove oil is very strong. You may want to use it in a very well ventilated area, or outdoors, and avoid getting it on your hands.

Many CKKs and some Koi hobbyists keep MS-222, also called Finquel, on hand for sedation and/or anesthesia. This is a MUCH better alternative, but costs more and can only be purchased from fish sources, unlike clove oil which can be found at your corner drug store.  Anesthetic dose of MS-222 is 50-100 mg/liter. Use 10 times this dose for euthanasia.  Whatever you are using, K.O.I. recommends leaving the fish in the solution for an hour after it has stopped respirations.


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