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Old 04-09-2006, 01:14 PM   #1
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An Overview of Euthanasia

Euthanasia: An Overview
By: Devilishturtles

What is Euthanasia, and why should we consider it?

As aquarium hobbyists, we have a responsibility to care for the fish we take into our tanks. However, sometimes there simply comes a time when we cannot take care of them any longer. Old age. Illnesses. Untreatable tumors. Infections. You name it. Not all are curable, and sometimes the quality of life issue must come into play.

First off, let’s define Euthanasia. The Merriam-Webster Dictionary defines euthanasia as: the act or practice of killing or permitting the death of hopelessly sick or injured individuals (as persons or domestic animals) in a relatively painless way for reasons of mercy. It couldn’t have been put better, in my opinion. The key words here are painless and reasons of mercy.

I know it’s hard, but sometimes a hobbyist must look past the present condition of their animal and consider a few key points. Will my fish get better? Do I have the means to make it better? Is the illness that my fish has, even treatable? Is its quality of life acceptable? Can I stand to watch it suffer any longer? If you answer no to these questions, it may be time to consider euthanasia.

It is also normal to feel grief afterwards. You may feel guilty, thinking that maybe you didn’t do all that you could to save the fish. You may feel regret, sadness, etc. Sadly, these are all normal feelings, and don’t differ much from when we have to put down a cat or dog. Fish can definitely become part of the family, which is why you should never hesitate on making the right decision.

How on earth do I do it?

There are a number of ways to perform the deed…sadly, many of these ways remain out of ethical standards, and are often misunderstood. I hope to clear up a few common misconceptions regarding the methods of euthanasia.

Methods listed are in order of least humane, to most humane.


This method should never be employed, for a number of reasons.

1. It doesn’t kill the fish, at least not for a very long time.
2. Fish are accustomed to water current. Many people believe that the forceful water movement of a flushing toilet will kill fish. Wrong.
3. After the fish has taken a ride through your pipes, it will end up in the sewer, still alive, where it will die a slow and painful death, succumbing to chlorine poisoning, and poisoning by other harsh chemicals and cleaning products.

Pure Alcohol

100% vodka or tequila works best. Get a cup, and simply drop the fish in it.

May or may not be completely humane. Studies suggest that alcohol severely burns the gills in the few seconds before death by respiratory failure. Otherwise, it acts a high dosage anesthetic, paralyzing and knocking the fish unconscious almost instantly.

Blunt Force Trauma (aka Smacking with a hammer)

Basically, this method is what it sounds like: causing a forceful trauma to the head of the fish, fatally damaging the central nervous system. There are a few ethical issues with this method however it can be humane if done correctly.

1. This method is best for large fish, the reason being that a larger fish is more easily handled than a smaller fish. Smaller fish have a tendency to flop around.
2. You must consider the stress it causes the fish to be first taken out of the water, handled by you, placed on a hard surface, covered with a material, and then smacked.
3. Sometimes, you aren’t always the most accurate of hobbyists. If you miss, even just slightly, it can cause for a bloody mess, and a floppy fish that is in incomprehensible pain.


This is a touchy one. There are many who believe that decapitation is not a humane way to go, because brain activity will continue until upwards of a minute after decapitation.

The method is simple, and very similar to the blunt trauma method. Take the fish out, place it against a hard surface, and take a very sharp knife to its head, making as clean a cut as possible. Stress may come prior to the act, in the process of setting up. The fish must be taken out of water and handled by you, all stressful activities. Keeping the fish still while you perform the act will also prove to be a challenge. This method is humane, as long as the person doing it can assure themselves that they can do it with as little stress to the fish as possible, but there are better ways.


This method can be carried out by simply getting a container of tank water with fish in it, covering it, and putting it into the freezer. There are however, certain humane issues with this method as well.

1. Most tropical fish are not known to enter a dormancy stage when in extreme cold. The same thing that happens in humans happens in fish. The body severely constricts the blood vessels, starting from the extremities, to keep the center of the body warm. This action that the body takes is extremely long and painful, and thus is also long and painful for fish.
2. Coldwater fish however, are proven to have a dormancy stage. This is the same stage that allows them to hibernate in freezing water over the winter in ponds. Their body shuts down, metabolism all but stops, and the method is painless, for the most part. (Note that after the freezeing is done, the fish should be decapitated)
3. A freezer drops temperature very quickly, about a degree every few minutes. This is too fast for this method to be completely humane to both cold water and tropical fish.
4. Ice crystals will form in the blood stream and cells, causing extreme pain to the fish.

A much better method than freezing, is the temperature shock method.

Temperature Shock, Freezing

100% humane, and the best way to go when euthanizing tropical fish.

The method is simple. Freeze a bowl of water until it has ice chunks in it, but is not solid in any way. Net the fish out of your tank and into the bowl. The difference in water temperature will cause an instant and fatal shock to the internal organs and nervous system of the fish. Sound harsh, but the deed is done painlessly and instantly. Make sure that the water is frozen sufficiently for this to be humane. Being impatient and dropping the fish in very cold, but not half frozen water, will only torture it.

Whenever someone asks my opinion on euthanasia, this is the method I suggest. It is the easiest to perform for the average hobbyist, and is instant.

Temperature Shock, Boiling

Again, 100% humane, the same method as above in regards to freezing shock, except you use boiling water. This method is recommended for cold water fish, instead of tropical fish, for obvious reasons. The temperature shock instantly shuts down all organs and the nervous system of the fish, painlessly. We do the same thing to lobsters when they are cooked. As always, use caution when working with boiling liquids. They won’t kill you, but will sure leave some nasty burns.

The same disclaimer as above. Make sure the water is at a good boil before employing. Dropping the fish in simply hot water, will not suffice.

Clove Oil (eugenol)

Clove Oil can be found relatively cheap in most health food stores, specialty food stores, and pharmacies. Mix it with warm tank water, and shake. Note, that the Oil is not readily dissolved in water, which is why the shaking is very important. The water will eventually turn white when the correct amount of clove oil has been added. Add the fish to this mixture, and it will slowly die from an overdose of this anesthetic oil. More clove oil may need to be added after the fish is in the solution, so my advice is to not skimp on the initial mixture. ¼ teaspoon per gallon of water is the lethal dosage, however more may be used.

After the fish appears dead, it would be best to either freeze the fish or decapitate it, as fish have been known to “wake up” after deep sleep, and supposed death from anesthetics.

Finquel/MS-222 (tricaine methanesulfonate) or Benzocaine

MS-222 is a medicine that can only be aquired from a veterinarian, or occasionally found over the internet. This method is completely natural, working just like an overdose with an anesthetic. The white powder of MS-222 is simply mixed in water, and the fish put in the container. Death will occur instantly. Obtaining it may not be easy, but is the best option by far, if available.

Benzocaine, like MS-222 is also instant, but this medicine is much less soluble in water, making MS-222 a much better option.

Note: This method is out of the question for the vast majority of us. There are other ways that are just as humane, however this method may be used for your own ethical reasons, or if you’d prefer a professional to do it for you.

Other methods that may be suggested to you, that are NOT a good idea

There are other methods that I’ve found mentioned, that are simply unacceptable. You should NEVER seek to euthanize a fish in any of these ways. There are much better options.

1. Alka-Seltzer or Baking Powder/ CO2 poisoning.
2. Suffocation (taking the fish out of water)
3. Bleeding to death (this involves taking a knife and cutting out gill filaments until the fish bleeds to death, can you see the obvious reason why this isn’t a good idea?)
4. Chemical Poisoning (bleach, detergent, soap, etc.)
5. Feeding the ill fish to a larger fish (do you want your larger fish to become sick too?)


Immersing any fish in a liquid may cause initial “excitement” as inhibitory neurons are depressed prior to reaching complete anesthesia. This is completely normal, and not painful. After the fish is unconcious, make sure to follow up by decapitation or freezing.

Now that I’ve done it, what do I do with the fish?

There are many options to explore. You may wish to have a memorial for you fish. Burying in the back yard is a good way to remember your lost pet. It may also help relieve some of that grief and guilt you are feeling.

If you’d rather not, there are other simple means you can take to dispose of the fish.

You can throw it in the trash (best to place it in a plastic bag first. Dead fish isn’t a pleasant smell), flush it down the toilet (only if a small fish), or burn it. All are safe methods of elimination.

These methods were researched and wrote up by the author. If you have any questions about what method is right for you, or if you have questions concerns or comments, please reply to this post, post your question in the Unhealthy Fish Forum, or send the author a PM.


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