Fish, Tanks and Ponds

Fish, Tanks and Ponds
A comprehensive guide to fish

Sedation, anaesthesia and euthanasia

The fish in the video clip was not euthanised, it was sedated in order to treat a facial ulcer. The clip was deliberately edited to appear ambiguous for use on this page.

Oil of Cloves

For the hobbyist the only connection between these three treatments is Oil of cloves. Commercial fish anaesthetics are only available to qualified vets and few others. They are not available to the general public. Some compounds used for sedation only are available See Treatment finder.
Oil of cloves can be used as a replacement for the commercial treatments and it can be used to sedate, anaesthetise and euthanise when the dosage is altered appropriately. The disadvantage when using oil of cloves rather than a purpose made product is that oil of cloves is:

  • Poor solubility in water.
  • Fast induction rate
  • Narrow field of safety.
  • Long recovery period.

The first of these problems is easily overcome by dissolving the required dose of oil of cloves in a small volume of warm water by vigorous shaking before adding it to the fishes water. The other problems can be overcome by taking great care and concentrating on what you are doing.


In order to calm a large fish such as a Koi or a large cichlid to prevent them from harming themselves and to allow proper inspection of the treatment area it is important that the fish is properly sedated. There are commercial products for this (usually sold by Koi dealers) or you can use oil of cloves. The commercial products will come with a set of instructions, follow these to the letter. Or if you use oil of cloves the dosage for sedation is:

  • Dosage for oil of cloves - 2 to 4 drops per 5 litres for sedation.

If the water is hard and alkaline or at low temperatures use the higher dosage, if the water is very soft and acidic or at high temperatures (tropical fish) use the lower dosage.

A fish under medium sedation will still be able to respond to some stimuli. maintain its equilibrium, there will be a decrease in activity and its breathing will be shallow.


There is only one option for anaesthesia of fish by a hobbyist - oil of cloves.

  • Dosage of oil of cloves for anaesthesia - 4 to 6 drops per 5 litres of water.

If the water is hard and alkaline or at low temperatures use the higher dosage, if the water is very soft and acidic or at high temperatures (tropical fish) use the lower dosage.

A fish under anaesthesia will lose its equilibrium, very shallow breathing, no response to stimuli. Keep a very close eye on the fish's breathing and do not wait until breathing stops or the fish may not recover.


There is no need to rush the treatment, most fish will live out of water longer than you think especially when sedated and kept moist. For large and medium sized fish it is possible to use a small water pump with a suitably sized pipe attached to irrigate the gills while the fish is submerged in order to get some fresh oxygenated water over the gills. This isn't really possible with very small fish so they will need placing near to good water movement. Recovery varies from fish to fish but most come to within two or three minutes.


Oil of cloves is the only option for hobbyist to euthanise a terminally sick fish.

  • Dosage for euthanasia - 20 - 50 drops per 5 litres of water.

Leave the fish in the solution for at least 30 minutes. Death normally occurs after just a couple of minutes but by leaving the fish in the solution it ensures that it is properly dead and with no chance of recovery.

There are one or two myths in circulation about using oil of cloves for euthanasia:

  • Alcohol makes oil of clove dissolve better in water.
    True - it does. But alcohol is a severe irritant to the fish and it will really struggle indicating that it is under great stress. A small amount of warm water with the oil of cloves added and shaken vigorously will be just as effective and cause no stress to the fish.
  • Oil of cloves sedates the fish but alcohol is needed to kill it.
    Utter rubbish.


Sedation is the mildest form of anaesthesia and it is used to calm a fish before and during treatment. It is extremely useful when large or nervous fish have to be caught in order to effect a treatment so that the fish is at less risk from harming itself.

Anaesthesia removes sensation from the subject and prevents pain in doing so. It should only used when absolutely necessary because the fish is at great risk in the hands of even a very experienced amateur when anaesthesia is used. It should only be used to prevent the fish from excess suffering when a particularly painful treatment is called for such as minor surgery to remove a dislodged and infected scale or the removal of multiple parasite from a leech infestation for example.

Euthanasia is a sensitive subject for most people but there are times when it has to be considered rather than let unnecessary suffering continue when there is no hope of the fish making a recovery. Try to look at it as a final act of kindness for an old friend. Please don't take the attitude that where there is life there is hope because that may lead to untold suffering which is completely unnecessary to a terminally ill or incurable fish.