Fish euthanasia

Fish euthanasia

Unfortunately, every aquarist sometimes faces a choice - whether to continue to treat a very sick fish that has been suffering for a long time, or to euthanize a fish, shortening its suffering. This choice is often very difficult, even for long-term fish owners, especially when the choice concerns a live creature which has been swimming in the aquarium for a long time.


Unfortunately, when there is no way out, we have a very sick fish and we are not able to restore it to health, euthanasia is the solution. Nobody enjoys watching dying fish.

However, is there an appropriate, humane method of killing a fish so that it does not tire, and is bloodless and non-violent at the same time? Below are the methods used by aquarists t. Unfortunately, some practices are unacceptable and recommended in pet stores (!).

Crushing the brain

The method is recommended for all species. It consists in crushing the animal's head very quickly. Unfortunately, this method is quite brutal and the aquarists with weaker nerves are not able to do it. Larger fish species can be killed by this method with a heavy object such as a stone.

This method causes the immediate death of the fish.

Decapitation - cutting off the head

Considered the most brutal and bloody form of euthanizing fish. Incorrectly associated with "murder". It consists in placing the fish on a wet surface (e.g. on a cloth) and quickly cutting off the head.

A heavy, sharp object such as a knife breaks the spinal cord in a second and the fish instantly die without unnecessary torment. This method of euthanizing fish is found by many fish owners as the best, fastest and, therefore, the most humane. It can be used for all species.

This method causes the immediate death of the fish.

A hard hit to the head

It consists in hitting a fish's head with a blunt, heavy object that will stun it. A method used to kill large fish species but unfortunately not always effective. Decapitation should be applied after hitting the fish.

If successful, this method of euthanizing fish kills them immediately. Not always fully effective when using too little force or too light object. For smaller fish species, the easiest solution is to wrap the small fish in a cloth and hit its head on the floor or the toilet bowl.

Draining in the toilet

Unfortunately, the most common method of getting rid of a fish. It doesn't really cause death. It can be compared to sending your pet on a long journey of imminent death through torment. Fish that are drained in the toilet bowl immediately meet detergents and feces in the drain pipes. As a result, your beloved pet lives for several hours floating in the sewage.

This painful process is unacceptable and inhumane method.


The method consists in putting the fish into a vessel (e.g. a jar) and placing it in the freezer. According to many, especially young and inexperienced aquarists, the most humane way of euthanizing fish.

Unfortunately, the use of the ice bath causes agony for the animal. Ice water cools down the fish first. The ice crystals that form then tear apart every cell in the fish's body.

Death occurs in terrible torments for the aquarium fish. In addition, the painful process takes quite a long time, which causes a prolonged and painful death. This method is not recommended for any animal.


Pouring with cold salt solution

The method consists in making a salt solution that can be cooled to a temperature below zero at home, and then pouring the "freezing" solution over the fish.

Death of the aquarium fish occurs faster with such an ice bath than when frozen, but it is very painful for the fish. Flooding the animal with such a solution causes thermal and chemical shock. In addition, the fish's body from the outside is quickly torn apart by the formation of ice crystals in the cells.

Even though the method of killing fish is faster than freezing, it is just as inhumane.

Pouring boiling water

It consists in pouring boiling or warm water over the fish or throwing it into the boiling water.

The method of boiling water is reprehensible. It causes a quick, but very painful death. The fish, when released into the hot water, press the fish's gills to the body in order to spare oxygen, which prolongs consciousness. It is one of the most cruel methods of killing fish . Proteins contained in the fish tissue s become stiff, causing pain in the entire fish's body.

The clove oil method

It is a method that is still being researched, but so far using the clove oil mixture is considered as one of the humane methods. Mix a few drops of clove oil with 20 ml of water, pour the clove oil mixture into the container with the aquarium fish. After 10-15 minutes, the clove oil mixture drops anesthetize fish. Pour another 15 drops of the clove oil mixture into the container. After 10 minutes, the fish falls asleep feeling no pain.

Overdosing carbon dioxide

Some aquarists decide to inject carbon dioxide to the aquarium water in large amounts. This is not acceptable method in terms of humane methods. Injecting too much of CO2 will only cause slow dying of the suffocating fish.

Removing fish from the aquarium water

Some people think that it's better to remain the fish for the natural death than to kill fish by the fish keeper. Be aware that fish feels pain, stress, discomfort and speeding up its death is not a murder but is a very humane way of helping the fish in agony. The aquarium fish left outside the fish tank will simply suffocate itself.

Dangerous impact of fish diseases on human life

In case of some serious diseases, the euthanasia of fish has its other equally important justification, because there are bacteria, viruses and fungi that can also be transmitted to humans. One of such diseases is Mycobacteriosis, a very dangerous bacterial disease that infects humans through, for example, skin damage (abrasions, cuts, bites, wounds). Then, ulcerative skin lesions form on the human skin. Therefore, when noticing any diseases in the aquarium (when putting your hands in it), you should always use protective gloves, especially when there are skin damages on your hands. In addition, you should also be careful not to rub your eye with a wet hand. In this situation, the right choice is to humanely euthanize a fish.

What to do if your aquarium fish is found already dead in the fish tank?

This is a quick answer: Take the dead fish as soon as possible outside the tank. If the dead fish is floating on the water surface, it means that it releases toxic compounds due to decomposition of the organic matter. And this means that it's poisoning the aquarium water where other fish swim.

When a fish dies and is not removed from the aquarium, it to some extent disturbs the biological balance in the aquarium, changing the physicochemical properties of the aquarium water. During the decomposition of fish, the pH values, as well as the content of nitrates, fluctuate. The content of water-soluble substances also changes in the initial phase, while in the final phase of decomposition it increases. Similarly, the content of nitrite fluctuates in the initial phase of decomposition, while in the final phase the level of nitrite decreases. The level of ammonia / ammonium ions increases from the initial to the final decomposition phase. And here the well-known rule is confirmed that when something dies in an aquarium, the level of ammonia rises. From the moment the dead fish are no longer visible and other fish, plants and microorganisms have absorbed the decomposition products, the ammonia / ammonium levels gradually decrease.

Of course there are very sensitive aquarium fish species to different swings in water parameters, mostly pH. That's why we recommend to take out the dead fish immediately. Some underwater ecosystems can manage the fluctuations in aquarium water parameters, other don't.


We strongly hope that this article shown you how humanely euthanize your fish. If we can recommend any method of euthanizing fish, using clove oil decapitation and crushing the brain would be the most humane methods because they end fish's life immediately. Of course, the choice belongs to the owner but choosing an acceptable method won't cause a slow death of your beloved pet. Other methods in this article used by aquarists are cruel and don't humanely euthanize aquarium fish. Animal euthanasia is increasingly explored by animal owners, including aquarium fish. American Veterinary Medical Association is still researching this topic, and if you want to learn more, visit their website where they publish the latest research on the subject.

However, we hope that you enjoy healthy fish in your fish tank and entering this article is only the matter of curiosity.