How To Euthanize A Fish – 1 Humane (and 7 Others MEthods To Avoid)

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Losing a pet is never easy, but losing a fish can really be hard! Many tropical fish have long lifespans which means they share a lot of time with us. Though we might not be able to interact with these animals in the ways we do with others, there’s still a deep bond.

Unfortunately, fish die. Whether this is due to stress, illness, injury, or old age, there will come a time when you are with your fish in its last days. At this point, you may need to humanely euthanize your fish.

There are a few ways to make this transition as peaceful and painless as possible. Let’s look out how to euthanize a fish.

Key Takeaways

  • It’s never easy saying goodbye to a pet, but some aquarium fish are especially near and dear to our hearts.
  • Always try your best to save your fish. Even fish on the brink of death have been able to make a full recovery given immediate and extreme treatment.
  • If you’ve done everything you can for your aquarium fish, then it may be time to humanely euthanize them.
  • Administering clove oil is currently the most recommended method to humanely euthanize your fish.

Signs Your Fish Is Dying

It’s important to note that euthanizing fish should only be used as a last resort. These methods are meant to help a fish move on when it has no more fight left to give. Until then, you should try to save your fish in every way possible.

If it’s your fish’s time, then there’s not much you can do besides make things easier. But how do you know it’s time to make that decision?

Aquarium fish are very resilient. Many species have been bred in the aquarium hobby for decades, leading them to survive some of the most common diseases time after time. There are a few symptoms that could mean your fish is in its last days, though.

  1. Laying on the substrate. Aquarium fish should never find themselves at the bottom of the tank. A fish that’s lying on its side at the bottom of the tank is likely exhausted and unable to hold itself up. However, if your fish still swims away when disturbed, there is a chance that you can save it with immediate and extreme treatment methods.
  2. Gasping for air. This usually goes hand in hand with laying on the substrate. Gasping for air is commonly a sign of affected gills, trauma, or a compromised immune system. At the same time, rapid gill movement can also be present in an upright-swimming fish. In most cases, this is a sign of poor water quality and can be reversed through large, scheduled water changes.
  3. Getting stuck in aquarium equipment. One of the most notorious aquarium fish for getting stuck in equipment is the neon tetra. If your fish gets pulled in by an intake valve, then it was most likely already sick. Unfortunately, this may not immediately kill the fish and lead to a slow death.
  4. Discolored and tattered appearance. Almost any fish that isn’t healthy will display signs of discoloration. A dying fish may be ghostly white with cuts and scrapes across its body and fins. Though this damage may look intense, as long as your pet fish is swimming, there is a chance to save it.
  5. Bullied by other fish and invertebrates. Even healthy fish can be bullied by other tank mates if not in ideal aquarium conditions. But a sick fish that has trouble escaping from harassment may be a sign that its health is quickly deteriorating. If the fish can be saved, it’s recommended to remove them to a quarantine system as quickly as possible.
  6. Abnormal behavior. Lastly, abnormal behavior can be a sign that your fish’s life is coming to an end. This can mean lethargy, lack of appetite, or swimming around in the front of the tank once the aquarium lights have gone out.

Many of these symptoms happen at the same time and overlap. They can be caused by a plethora of diseases, illnesses, parasites, and infections. Some fish might even experience two or more serious ailments at the same time. Try to find the cause behind your sick fish and treat it accordingly as soon as you can.

In most cases, this involves setting up a quarantine system and dosing medications. It can also mean frequent water changes, dips, and temperature gauging. Some fish owners might even perform surgery on their fish before they give up on their pet.

If you’ve tried everything and your pet fish still doesn’t recover, then it’s time to look at how to euthanize a fish in the most humane ways possible.

Most Humane Ways

It’s not easy to know when to euthanize your fish, but it’s important to know how to do it just in case it becomes necessary. Euthanizing fish is a highly debated topic within the aquarium hobby. Some fish owners think the act should be quick and fast while others think it’s best to lull the fish to sleep using either chemicals or temperature differences.

Though we won’t go into the morality of the topic, we do believe there are some better and more humane methods than others. The American Veterinary Medical Association (AVMA) recommends several solution-based euthanization methods1, including prescribed anesthetics and clove oil dosing.

Some of these fish euthanasia methods do require additional supplies. Keep in mind that by the time you purchase the items needed to humanely kill your fish, the opportunity may already have passed.

1. Clove Oil

As of right now, the clove oil method seems to be the most effective and gentlest way to euthanize a fish. Clove oil is an aromatic oil that is extracted from flowers from a clove tree (Syzygium aromaticum). It can readily be found at local grocery stores or pharmacies.

Clove Oil Display

Clove oil works as a sedative for aquarium fish. In fact, some fish owners use lower doses of clove oil to cause the fish to be temporarily sedated for surgery. In larger doses, clove oil becomes deadly.

Simply place the dying fish in a container. Mix some tank water with the 10 drops of clove oil in a separate container. Combine the milky-white clove oil mixture in the container holding your fish. Shortly after, your fish should be sedated. If another few minutes pass and your fish is still breathing, add 5 more drops. Continue this until your fish has slipped away.

Unfortunately, clove oil isn’t very soluble in water. For the best and most concentrated effects, it’s best to administer the clove oil into the fish with a syringe. However, if you don’t have a syringe, then the clove oil water mix will work just as well.

This method is the current preferred method for euthanizing a fish for most hobbyists. It allows the fish to lose consciousness and quickly pass.

Clove Oil and Alka Seltzer

To make sure that the clove oil method is completely effective, it’s recommended to follow dosing with alka seltzer. Using clove oil alone for euthanizing fish can take a while, and it’s possible that your fish wakes up after a long sleep.

Alka seltzer works by introducing carbon dioxide into the water and expelling oxygen, leaving your fish with no air to breathe. It is not recommended to dose alka seltzer alone as suffocating can be painful for the fish.

2. Prescribed Anesthetics

If you have access to medical anesthetics, then they should be used to humanely euthanize your fish. Some of these concentrations include benzocaine hydrochloride and tricaine methanesulfonate.

Of course, very few hobbyists have access to these solutions. However, they are some of the best ways to euthanize your fish according to the American Veterinary Medical Association.

In the same way clove oil works, an overdose of prescribed anesthetics causes the sick fish to lose consciousness until it gently slips away.

3. Barbiturates

Another way a medical professional might euthanize a fish is by injecting it with barbiturates, or a depressant drug. This helps the fish relax and eventually pass away. Like prescribed anesthetics, barbiturates can only be obtained in a professional medical setting.

Inhumane Ways

Unfortunately, the best ways of how to euthanize a fish have been found through trial and error. Aquarium fish feel more than we think, and we’re still figuring out how to make their transition painless. Through the years, fish owners have discovered methods that cause painful death.

How can you tell that an aquarium fish is suffering during euthanization?

It’s hard to read a fish’s body, especially if they’ve been sick. However, a peaceful death should be quiet and relaxed. The fish should not react to what’s happening. If the fish’s behavior changes in any way, like gasping for air, sudden body movements, trying to escape the container or frantic swimming, then they are probably experiencing a slow death.

No matter which method of euthanization you choose to help your sick fish with, always make sure that it’s painless. That being said, here are some of the ways to not try euthanizing fish.

1. Stun and Sever

If chemical products or medications aren’t available, some hobbyists might resort to brute force to kill fish. This is never recommended, especially when performed in a volatile manner.

Unfortunately, many videos have been made popular due to hobbyists slamming their tropical fish on a hard surface to stun them and then severing them. Many things can go wrong during this lengthy process, all while your fish may still be awake.

2. Decapitation

Similarly, some hobbyists use a sharp knife or hammer to quickly end their fish’s life. While this is definitely more humane than brutally stunning and severing the fish, decapitation can still result in failure which causes unnecessary pain.

Though we list decapitation as an inhumane method of euthanizing fish, as long as you can guarantee a quick and painless death, this method is one of the best.

3. Ice Water Bath

Another common method of how to euthanize a fish used to be an ice bath or freezing the fish. For the most part, this was considered humane before hobbyists knew how painful this could actually be. The theory was that the fish’s bodily processes would slow down until they were unable to work altogether.

The truth is that ice crystals slowly form in the fish’s bloodstream and cells and become very painful. This is a slow death and your fish feels the majority of it.

4. Flushing Down The Toilet

You’ve probably seen it in movies: flushing a pet fish down the toilet once it’s gone belly up.

No matter which way you put it, live or dead fish are not supposed to enter the sewage system. If you have any doubt as to whether your fish is alive or dead, do not flush it down the toilet! And do not flush your fish down the toilet once it has died either.

Toilet Flush

If you flush a dying fish, you’ll cause a hard death. There are a few things that can kill your fish once you flush it down the toilet.

First, is water temperature. Toilets have cold water. A sick and dying fish will quickly succumb to a difference in water temperatures. Next, chlorine will help kill your fish. Chlorine is toxic and typically needs to be removed from a fish tank. However, toilet water contains chlorine, which will quickly burn the gills and internal organs of your fish.

If the temperature or chemicals don’t get your fish, then they’ll die due to other bacteria and water treatments.

5. Carbon Dioxide

There are a few ways a fish can be killed with carbon dioxide, but none of them are recommended. Any death by carbon dioxide (CO2) is through suffocation, which is a long and painful experience for the fish.

Cold Break CO2 Tank

The first method of killing fish through carbon dioxide is by placing an alka seltzer in the water without any other anesthetic. As mentioned before, this is a good method when used together with a sedative, but alone, causes CO2 to fill the water and expel oxygen.

Similarly, some hobbyists pump pure carbon dioxide directly into the water. These pumps are available for planted aquariums but can be used for overdose as well. This method is very difficult to gauge and can be pretty costly!

Related to carbon dioxide suffocation, some fish owners simply remove their fish from the water altogether. Fish cannot process atmospheric air and they suffocate, which also takes a considerable amount of time.

6. Boiling Water

While boiling water is an acceptable method to kill lobster and crabs (though, it shouldn’t be), heating your fish up to the point of death is also inhumane. Some hobbyists have poured boiling water over their fish while others have boiled the water with the sick fish in it.

No matter the method, using hot water to kill fish is incredibly painful. When placed in hot temperature, the fish’s gills close. This allows them to keep consciousness for longer than you might think. Proteins in the fish’s body also become stiff over time, which is felt by the fish.

7. Alcohol

Killing fish with alcohol, namely ethanol, is one of the most controversial methods currently in conversation. This is because fish don’t seem to react much when placed in alcohol.

However, the process isn’t completely painless and that’s why we don’t recommend it alone. Instead, first use an anesthetic, like clove oil, and then follow with alcohol to ensure that the fish has died.

How Do You Know Your Fish Has Passed?

It’s easy to spot a dead fish, but it’s harder to tell when a dying fish has turned into a dead fish. No, cartoon x’s won’t appear over their eyes and they won’t go belly up at the water surface.

Instead, gill movement will stop. The eyes will sink and the pupils will be fixed and sometimes dilated. There will be no reaction when you touch the fish and the body will soon become stiff.

If you ever doubt that your fish is dead with one of these methods, continue to add the given solution. Also, wait at least 10 minutes before additional doses to ensure they have time to take effect.

What Do You Do With A Dead Fish?

When you’re certain your fish has died, place it in a plastic bag and put it in the garbage or hold a funeral in your backyard. If you have the means, you may also cremate your dead fish. This is especially preferred if the fish suffered from extreme disease or illness.


If you’re looking up how to euthanize a fish humanely, it’s most likely time for your fish to go. Before you say goodbye to your pet fish though, make sure that you’ve done everything you possibly can to save its life. If there’s nothing more you can do, administer clove oil as this is the current most painless way to euthanize fish. Then, take time to appreciate your fish’s life and everything they gave to you.

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