Euthanizing Aquarium Fish

1. Do you have a reasonable diagnosis for your fish?

As hobbyists, we rarely have access to scientific equipment to help us determine a diagnosis for our sick fish. Most of us aren't fortunate enough to have a microscope or other necessities to distinguish between bacterial, viral or parasitic infections. In most cases, we make assumptions based on probability. If your fish has a bloated abdomen and the scales are protruding, it is reasonable to assume he has Dropsy, which is rarely curable in tropical fish like Bettas. The degradation of the fish can be quick or slow with Dropsy and the final stages often leave the fish helpless and gasping at the bottom of the tank. Utilize your recourses to come up with a diagnosis. You can try books, the internet, your LFS staff or other hobbyists.

2. Have you exhausted your treatment options?

Few diseases are as straight forward as Dropsy and many can be easily cured with good water conditions and inexpensive over the counter aquarium fish medications. As a pet owner, it is your responsibility to treat your sick fish appropriately. Once you come up with a reasonable diagnosis, treatment is a two part process. First, discover and fix the cause. (Poor water quality is often the culprit) Secondly, treat the illness itself. (antibiotics, antiparasitics, temperature control, etc.) Treatments can take time and effort and let's not forget that the fish's own immune system will work to combat disease as well. Most common fish illnesses ARE curable.

3. Does your fish still have the will to live?

Ok, this can be a little tricky to determine. My personal recommendation, take it or leave it, is if the fish tries to allude capture he still has the will to live. If he tries to swim away when you go to net him, then he is still utilizing his fight / flight response. If the fish allows you to scoop him up, he may be too far gone to save. Still, this isn't 100% confirmation that the fish should be euthanized. I personally have had a Betta splendens that was so sick you could scoop him up with your hand, but because I was too squeamish to euthanize him my only option was to treat for the illness and wait until he succumbed. Remarkably, the Betta recovered fully and lived another year and a half. On the other hand, there have been many that I have been unable to save. This is ultimately your judgment call. Consider the physical state of the fish, the suspected illness and the age of the fish. A two year old Betta may recover fine and live for another two years. A 5 year old Betta is already nearing the end of his natural lifecycle.

How to Humanely Euthanaize a Fish

There area several methods for aquarium fish euthanization frequently utilized by hobbyists but only a handful are considered humane. Unfortunately, some of the methods previously considered humane have decidedly been determined not to be so. Here are a few methods considered to be a safe and humane method for euthanizing fish.

1. MS 222 [Tricaine methanesulfonate]:

MS 222 is frequently used as anesthetic and a sedative for aquatic animals but in larger concentrations is the preferred method for euthanizing aquarium fish. It is approved by the FDA and considered humane by the American Veterinary Medical Association. It can be purchased through your vet or online. A bath with 250 mg of MS 222 per liter of water is adequate. The fish should be bathed for a full 10 minutes to assure death.

2. Benzocaine hydrochloride:
Benzocaine hydrochloride is similar to MS 222 and is a safe and humane method of fish euthanasia. A concentration of 250 mg per liter or more is effective for euthanasia. At this time I am uncertain of availability. Contact your Vet for more information.

3. Eugenol [Clove oil]:
Eugenol, the active ingredient in clove oil, is another sedative that when used in high doses is safe for fish euthanization. It is not approved by the American Veterinary Medical Association but is considered safe and humane by most aquarists. It can be purchased at your local pharmacy or in most health food stores. Being an oil, it does not dissolve in water. Once the oil is added to the water it must be shaken vigorously and the fish should be added immediately before the oil has the chance to separate. Doses greater than .25 ml per liter of water is adequate.

4. Decapitation:
While this can be the most difficult for the fish owner, it is considered humane and is the quickest euthanization method. Using a very sharp knife, detach the head from the spinal cord by cutting directly behind the gills. To avoid stress and discomfort associated with removal from the water, utilizing one of the above mentioned methods for anesthetization may be desirable.

Questionable Methods:

The use of Alka-Seltzer® tablets in water or high concentrations of Ethanol (AKA the Vodka Method) will cause death but it is not known to be free of pain and suffering. It is likely that these methods are humane when dosed properly. At least two tablets of Alka-Seltzer® per liter of water or 30 ml pure grain alcohol per liter of water are the appropriate doses. Because fish frequently react physically to these methods it is unknown what, if anything, they are feeling. Because of this, these methods are considered inferior to the approved methods above.

Unacceptable Methods for Fish Euthanization:

1. Freezer Method:
Dropping your fish into freezing ice water or putting them in the freezer to slowly freeze (hypothermia method) does not quietly put your fish to sleep. In cold blooded animals, it is believed that the formation of ice crystals in the tissue may create discomfort or severe pain. The hypothermia method is never ok. Rapid freezing may be applied only if the fish is deeply anesthetized prior.

2. Flushing:
Flushing your fish down the toilet is not only cruel and inhumane, but it is also illegal. Flushed fish can survive for hours or even days exposed to horrific conditions and toxic water quality. Flushing sick fish can also contaminate your local water shed with aquatic diseases. This method is never appropriate.

3. Boiling:
Dropping your fish into boiling water is painful and does not cause instantaneous death. This method is not approved.

4. Other Methods:
There are dozens of other methods for fish euthanasia circulating among the hobby that are not considered humane. The ethics of euthanasia in general are often debated. If you determine that euthanizing your aquarium fish is necessary, please only consider humane methods that remove all pain and suffering from the equasion.

American Veterinary Medical Association, "2000 Report of teh AVMA Panel on Euthanasia."JAVMA. Vol 218, No. 5. 2001. http://www.avma.org/issues/animal_welfare/euthanasia.pdf

Dr. Harms, Craig. "Euthanasia in Fish." PetPlace.com. publishing date unknown. 12 Feb 2007 .