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Euthanasia is the deliberate ceasing of an animals life functions in a painless way so as to relive the suffering of the animal when medical aid has not helped. It is also used when culling fish that have a malformation or are not up to standards when breeding.

In the aquarium hobby various methods are used. Here is a current list.

Anesthetic Overdose[edit]

These include: Finquel, Tricaine methanesulfonate (TMS), Benzocaine hydrochloride, MS-222, etc. Pros:

Easy, and believed to be painless.


Can be difficult to find. Vet prescription often required.
If animal is removed too soon they can be revived.
Fish have shown a stress response to some of these chemicals.

Carbon dioxide[edit]

This can be put into the water via airstone, Sodium bicarbonate (Bicarbonate of soda, baking soda), health salts (Alka-Seltzer). It is not recommended for amphibians.


Easy, and painless.


Certain species of fish (surface breathers) and amphibians can survive in extremely low oxygen environments so the use of CO2 may not be a quick method for anaesthetising.

Clove oil[edit]

The fish must be out in its own container with water. Two doses of clove oil are prepared, one which will render the fish unconscious and one which will put it to sleep. The first does should be diluted, with about 5 drops per cup. Shake vigorously in a small container with water, then dab your finger and wipe your mouth with the solution. It should not sting or burn and if it does you should dilute the solution.

Once the fish has passed out prepare a much more concentrated mixture and pour it into the tank, should be done exactly the same as the first dose however there is no need to test its diluted-ness as it should be extremely concentrated Pros:

Quick, easy, and painless.


Some may have trouble finding it, as well as administering inadequate dosage.

Freezing or Boiling[edit]




May not be painless. Freezing not recommended for cold water species.



Easily available.


May not be painless, as it may burn the fish’s gills and might be a prolonged death

Physical violence[edit]

Examples: Sudden blunt trauma, Decapitation, Pithing, feeding to larger fish, etc.


If done properly can be quick.


If not done properly can cause the animal to suffer.
Most methods require the animal to be removed from the water first which stresses them.
Many owners may not be able to bring themselves to carry it out due to the unpleasant nature of the result

Flushing down the toilet[edit]


No special equipment needed.


Akin to putting a puppy in an outhouse.
Can introduce disease to your septic system and the environment.
Animal may not die.