How to euthanize a fish

How to Euthanize a Fish: Humane Euthanization

Losing a pet is never easy, especially when you have to make the choice to put them down. However, it is our responsibility as pet owners to act in our pet’s best interest. Learning how to euthanize a fish is part of responsible pet ownership.

If your fish is sick, suffering, or has a terminal condition that is causing it to suffer, it is probably time to put it down. 

Many people do not realize that euthanasia is an option for fish, but if your fish is in pain and slowly dying, it is a responsible option. Some people prefer to let “nature take its course” and allow the fish to die naturally. However, most people consider the fish’s quality of life in its last days in order to make the best decision.

Before you attempt to euthanize your fish, read this guide to learn how to euthanize your fish in a humane manner.

Recommended items for humane fish euthanization:


Why would you euthanize your pet fish?

Fish can get sick with diseases like ich, dropsy, and more. Aggressive tankmates can brutally injure your fish. Pests like hydra or planaria can seriously hurt or kill your fish. Human errors, like adding untreated tap water or failing to cycle your tank, can be fatal to our fish friends. In other words, there are many ways your wonderful pets can be harmed in their aquarium.

We hope these situations are rare but they do occur. As a responsible pet owner, it is important you’re prepared when the moment arrives. If your formerly healthy fish is now suffering, the most humane response is to end their suffering by euthanizing them.

Euthanizing them, or humanely ending their life, can be done at the veterinarian’s office. However, this is the most expensive route.

Most aquarium owners choose to euthanize their own fish. As an aquarium owner, it is only a matter of time before the situation comes up where this duty is required. It may sound cruel or gruesome, but it is one of the most important skills as an aquarium owner. 


Is it time to euthanize your fish?

Honestly, if you’re asking this question in the first place, the answer is probably yes. 

But to be more specific, disease is a prime time for considering euthanasia. Common examples are fish with dropsy or severe ich, fish failing to respond to medications, fish that repeatedly go through bouts of disease, and old fish which are easy targets for infectious pathogens. A dying fish should be put out of its misery.

A second potential issue is major stress. Stress can kill fish and reduce their will to live. Fish are focused on the basics of survival—finding food, escaping predators, and engaging in procreation. When a fish is unable to do these things, they will be under major stress. In some cases, this stress will outright kill a fish. In some cases, this stress will cumulatively wear a fish down over time. The question then is not if the fish should or will die, but when and how quickly that death will occur. An example of a stressful situation would be a fish with a damaged fin that won’t directly kill it, but will severely limit its ability to participate in everyday activities. Euthanasia can be a humane option in these situations.


How to Humanely Euthanize Fish

Overdosing fish on prescription level anesthetics is the best way to give them a peaceful death. However, these drugs require access to a veterinarian who can order controlled substances and provide fish euthanasia. This is the most expensive way to put a fish down and not realistic for the general public. Most vets aren’t fish specialists and most fish keepers have more than one fish, making it cost-prohibitive long-term.

There are methods to euthanize fish with things that are readily available to the public. This is a controversial topic that’s endlessly debated online in aquarium forums. Death tends to bring out strong feelings in pet owners and the euthanization of fish is no different.

We explore some of the best ways to euthanize fish at home so that they don’t suffer needlessly. Make sure to read through everything to make sure you’re selecting the best method that you feel most comfortable with.

Clove Oil

Clove Oil is one of the most popular euthanization methods. It is our favorite method for ending the suffering of your fish. Clove oil is an essential oil derived from the Syzygium aromaticum plant. It contains an active ingredient called eugenol that has numbing properties. It is recommended by the American Veterinary Medical Association as a humane way to kill fish.

It essentially puts your fish to sleep before killing it, reducing any suffering. We recommend all fish keepers keep a bottle of clove oil stocked so you’re ready if the need arises.

One word of caution – make sure that you leave the fish exposed to the clove oil long enough. Clove oil is used to put fish to sleep for surgery so if you don’t do this process long enough, or with enough clove oil, your fish might just be deeply asleep and will wake back up once removed from the clove oil.

Our Recommendation: Clove Oil with Dropper

Our Pick
Now Essential Oil, Clove
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How to Use Clove Oil:

  1. Find two containers – one for the fish and one small container for the clove oil mixture (lid is recommended). Figure out how much water the fish container holds so you can dose the clove oil properly. Don’t add the fish yet.
  2. Fill the fish container with enough aquarium water so that the fish is comfortable will be comfortable.
  3. Add an airstone, airline, and pump so that there are bubbles in the water. This will also keep the clove oil dispersed in the water. 
  4. Grab your second jar and fill it halfway with warm water. This is your clove oil mixture jar.
  5. Use a medicine dropper to add clove oil into the second jar. Dosing is 0.5 ml (about 10 drops) per liter of water in the big container. That’s roughly 2 ml (½ teaspoon) per gallon.
  6. Put the lid on your jar and shake it vigorously. The liquid will become milky.
  7. Net the fish and place it in the large container.
  8. Slowly pour the clove oil mixture into the large container with the fish.
  9. The fish will calm down, then gently and quietly go to sleep, turning belly up.
  10. Leave the fish in the container for at least an hour to make sure that it has died.

Alka Seltzer / Baking Soda

Adding Alka Seltzer will also quickly euthanize a fish. Alka Seltzer causes an instant chemical reaction between the citric acid and the sodium bicarbonate (baking soda) that causes carbon dioxide (CO2) bubbles to rapidly form. The CO2 quickly depletes the oxygen in the tank, killing the fish.

This method works quickly. There is less risk of a fish reviving after this method than the clove oil method, but we recommend leaving the fish in the Alka Seltzer solution for at least 10 minutes to be safe. 

The downside to this method is that the fish will briefly thrash. Some believe that the fish does suffer briefly before it dies and therefore refuse to use this method. It will be aware of the decreasing amount of oxygen and that will cause stress in the final moments. Based on experience, the experience is typically limited to a few seconds at max before total stillness but it is important to be ready for the thrashing if you go this route.

For this reason, we prefer the clove oil method over Alka Seltzer. If you’re going to go this route, here is our recommendation for Alka Seltzer.

Our Pick
Alka-Seltzer Original Antacid and Analgesic
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How to Euthanize a Fish Using Alka-Seltzer:

  1. Fill a container with tank water, net your fish, and place it in the container.
  2. Add 8 tablets of Alka Seltzer per gallon of water.
  3. Tablets will fizz immediately as they dissolve. Fish will thrash briefly and then float to the top.
  4. Leave fish in the container for 10 minutes to ensure it is dead.

Euthanization Methods to Avoid

There are a lot of methods on the internet that are cruel, or have the potential to be very cruel, for euthanizing your fish. We cover the main methods to avoid below, and why you should strongly consider avoiding them (and tell your fellow fish keepers too!). Also, it is easy to euthanize your fish using clove oil so just do that! No pain involved, just a nice deep sleep. 

1. Decapitation

This one has potential to be a cruelty-free method. However, it requires precision and a strong stomach, because there will be blood flowing freely. 

Decapitation involves simply holding the fish on a flat surface and cleanly slicing its head off just behind the gills. If you can cut the fish’s head in a clean, swift motion, making sure you decapitate it instantly, this method is effective. 

However, if you are squeamish about blood or guts, this is not the method for you. If the fish is flopping, or your hand is not steady enough to cleanly and quickly decapitate it, you should use one of the above methods (clove oil or Alka Seltzer). 

How to euthanize a fish by taking out of water

2. Flushing

I grew up watching my mom flush several fish down the toilet. I was too little to know that this was not a good plan for disposing of fish. Flushing fish is not even a good option for dead fish, as it potentially exposes wild fish populations to whatever bacteria or virus killed the fish originally.

Flushing is not a quick or painless death. The fish will be shocked by the temperature and water chemistry changes, adding to their stress. The chlorine in the water can burn them. It will travel through a pipe, getting bumped and scraped, until it lands in a cesspool of human waste where it will eventually suffocate. If you’re struggling with actively killing your fish, it is better to let it die on its own in the tank than flush it down the toilet.

3. Ice Bath

This method involves preparing a container of ice water and then dumping the fish into the ice water, shocking it to death. This one has conflicting opinions if it is humane. Research tends to suggest it can be humane but depends on the fish size. For example, one study on Zebra Danios found that a cold water bath (less than 39 degrees Fahrenheit) can be humane. This method may work on tropical fish less than 2 inches so only consider this an option for smaller fish. Avoid this method with larger fish.

However, even for small fish, there is risk involved. if the ice touches the fish, ice crystals can form on the gills. This will cause a searing pain on your fish’s gills. This is not a comfortable situation for your fish’s last moments. This method is also not appropriate for cold-water tolerant fish, such as koi or goldfish. They can survive in cold temperatures so they will likely wonder why you’re making their water so chilly.

Also, the method of putting your fish in the freezer and waiting for it to freeze is clearly not a humane method. Freezing fish is not humane. Don’t do it.

4. Taking fish out of water

Removing the fish from water until it suffocates is a slow and painful way for your fish to die. Fish can breathe oxygen, but only when it is dissolved in water. Outside of water, your fish’s organs will slowly fail. This is a cruel way to kill your fish.

5. Smacking the fish on a hard surface

The idea here is that you energetically swing the fish and smack its head on a hard surface, instantly killing it. In theory, it could be humane but there is simply too much that could go wrong here. There is a high chance you won’t be able to kill the fish with a single, quick blow. The fish could be momentarily stunned, injured and in pain, or your grip could slip and it could go flying across your kitchen. 

6. Smashing the Fish’s Head

Another method to avoid. Good in theory but lots of ways it can go wrong in practice. 

To be successful, you have to completely crush the entire head of the fish with one quick stroke. However, if you miss, you just maimed the fish, and it will sit there, slowly suffocating, until you finish the job. There are better methods. Choose something else.

7. Vodka

There are two schools of thought here – a diluted alcohol bath that slowly intoxicates your fish until it dies or a very concentrated alcohol path that shocks it to death. Either way, an alcohol bath will kill your fish but it will also burn the gills during its final moments. Don’t do this to your fish.

8. Boiling Water

There are some reports of adding your fish to a boiling pot of water. In theory, this method is probably faster than an ice bath death. However, there is guaranteed to be some burning pain in the final moments. Don’t do this.


Verifying Death

It is important to verify death before disposing of your fish. The biggest sign is the gills. Check the gills for movement. If they’re not moving, the fish isn’t breathing. Bettas can breathe through their mouths so make sure to check their bodies for up and down motion. 

You can also look at the fish’s eyes. If the eyes are sunken, your fish is dead or near death. Also, check for cloudy pupils, which is also a sign of death in most aquarium fish.

You can also check for movement by gently touching your fish with the edge of the net. Most fish will make an attempt to move away if they’re alive.


How to Dispose of Dead Fish

We don’t recommend flushing dead fish, which can end up in local waterways. The bacteria, viruses, or parasites that killed them can then be passed to native fish. This can be devastating for local fish populations and cause new problems in wild populations.

Instead, we would recommend either burying your fish in your backyard (RIP Mr. Bubbles) or placing the fish in a plastic bag and disposing of it in the garbage.

As passionate aquarists, we want to protect all fish populations, both captive and wild. 


Fish Euthanization Conclusion

I hope this article has provided clarity about how to humanely euthanize your fish in a way that minimizes suffering.

The decision to euthanize a fish is never an easy one. If you’re reading this article, then you probably have a sick fish and you’re exploring what to do next because you don’t like watching it suffer.

As fish keepers, we can get very attached to our fish. Humanely euthanizing a fish (and pet) is never an easy choice but it is often the right choice. 

Your fish is lucky that you’re its caretaker and you’re exploring humane ways to end their suffering. We will wish you the best in whatever path you choose.

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