Humane Methods of Euthanasia for Fish

Euthanasia is a common procedure offered for dogs, cats, rabbits, and other pets that are frequent patients to veterinary clinics. However, when it comes to fish, little information is readily available regarding the possibility of euthanasia. Owners must conduct their own research, typically by visiting fish forums, fish websites, and other sources to acquire information. Although these sources can provide some answers, the information is not always accurate and may represent only the opinions of other fish owners. Fortunately, the AVMA Guidelines for the Euthanasia of Animals report published in 2007, accessible online at, reviewed and recognized humane methods of animal and fish euthanasia. Listed below are some of the more practical and AVMA-recognized methods of euthanizing fish.


The American Veterinary Medical Association (AVMA) recognizes two humane methods of euthanasia for fish: use of tricaine methanesulfonate, commonly referred to as TMS or MS-222, and decapitation

  • TMS is a white, powdered muscle relaxant that is mixed directly into the water. The AVMA suggests that larger fish be flushed on the undersides of the gills with TMS. TMS is acidic and needs to be buffered with sodium bicarbonate (baking soda) in the aquarium to maintain a neutral pH level. Without being buffered, the acidity of the compound can burn the fish and cause unnecessary distress. TMS can be purchased as is or as part of a product specifically made for fish euthanasia.
  • Decapitation is also deemed humane as long as it is followed by pithing, which is the destruction of the brain. After decapitation, insert a probe into the head and swish it around to destroy the central nervous system. Similar to a lobotomy, pithing is done because, unlike mammals, fish can remain conscious after decapitation due to their unique physiology. Cranial concussion, or stunning, prior to decapitation and/or pithing is also recommended. However, since this method requires skill and precision that might be challenging.

Some methods of euthanasia commonly discussed by fish owners include the use of clove oil, freezing, and carbon dioxide. None of these are recommended. Freezing has been shown not to induce loss of consciousness, so it may still cause distress to the animal. Carbon dioxide in water causes acidity in the water, and has been banned as a method of euthanasia in aquaculture in most countries because of the negative impact it has on fish welfare.

Based on the recognized methods of fish euthanasia, the simplest and most effective method is the use of TMS. Decapitation and pithing is a cost-effective, but potentially more challenging, method. Freezing and carbon dioxide use should be used only as a last resort. Effective euthanasia can reduce a beloved fish’s prolonged suffering.

Pauline Chen and Daniela Sharma, Ph.D. – Rutgers University