Euthanasia

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
These include: Finquel, Tricaine methanesulfonate (TMS), Benzocaine hydrochloride, MS-222, etc. Pros:
 * Easy, and believed to be painless.

Cons:
 * 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
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.

Pros:
 * Easy, and painless.

Cons:
 * 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
Pros:
 * Quick, easy, and painless.

Cons:
 * Some may have trouble finding it.

Freezing or Boiling
Pros:
 * Easy.

Cons:
 * May not be painless. Freezing not recommended for cold water species.

Alcohol
Pros:
 * Easily available.

Cons:
 * May not be painless.

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

Pros:
 * If done properly can be quick.

Cons:
 * 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.

Flushing down the toilet
Pros:
 * No special equipment needed.

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

Links

 * Wikipedia
 * The Gab on Euthanasia
 * FishDoc on Euthanasia Treatments
 * Euthanasia guidelines PDF file from the American Veterinary Medical Association’s (AVMA)
 * RSPCA and the use of CO2
 * The Krib on Euthanasia
 * Fish Slaughter, Killing, and Euthanasia
 * University of Washington Policy for the Euthanasia of Fish Species
 * Euthanasia for Amphibians
 * Don't Flush That Fish!
 * Time to rethink anaesthetics?