Are there health risks to leaving a dead fish in the aquarium?

Here’s the deal:

I understand how worrying it is to have a dead fish in your aquarium.

You might be asking yourself questions like ‘What should I do know?’. But before any of that, you should be familiar with the risks.

So, what are the risks? Here’s your answer:

Having a dead fish in your aquarium can spread fungal, parasitic and other infectious diseases to other fish in your aquarium. A dead fish that died of a disease can become a carrier of illnesses in a tank.

But what should you do now? How should you avoid the dead fish from affecting the other fish? Keep reading on to know more:

How Dead Fish Affect Other Fish And The Water

Dead fish can be lethal to all the remaining fish in a number of ways. Here are some of the risks associated with leaving a dead fish in your aquarium:

  • Leaving a dead fish in your aquarium can spread illnesses and diseases to other fish. This is because the dead fish was not removed from the tank in time. You may notice some unusual behaviour in your other fish too, as parasitic diseases can dramatically affect the brain it’s host.
  • Like any other living being, the fish, when it dies, would decompose. This decomposition would cause it to give off toxic chemicals like Cadaverine and Putrescene. All these toxic substances will pollute the water and it will start becoming unhabitable for the other fish. And the last thing you want for your other fish is to start consuming the decaying particles of the dead fish.
  • Even if your fish died of old age, the main risk would be the release of ammonia which will also pollute the water in your tank.
  • The other fish in the tank will react to the water being polluted, and so might die from being overstressed. Normally, fish die due to being over stressed when they are being kept in a small tank. And when the water is polluted, it would increase the stress level of the other fish risking their life.

The level of risk also mainly depends on how your fish died. The risk is higher if it died of infectious disease as other than the decaying toxic particles polluting the water, there is the risk of the disease spreading to other fish. But the risk is lower if the fish just died of old age or overstress as the only problem is the pollution of water by the decaying of the dead fish.

Nonetheless, it is not good to leave the dead fish just decaying there in the tank at any cost. Because of all the risks stated above, all of your other lovely fish are in danger and they might die if you don’t do something quick! 

What To Do With Your Dead Fish?

The very first thing you need to do after reading this article is to remove the fish as soon as possible. Talking from personal experience, it’s not very pleasant and is rather painful if your fish meant something to you.

You can use a fish net or gloved hands to take the dead fish out of the tank. It is not preferred to use your bare hands because of all the germs. Also, remove the toxins like ammonia from the water.

Now that the fish is out of the tank, place it in a paper bag before throwing it away. Another advantage of keeping the fish in the paper bag other than easy transport is that you won’t be able to see your dead fish’s face to make this process more painful.

One more thing:

If you were really attached to your fish and if you genuinely loved it, I would not recommend you to just flush it away or throw it in the trash. It would be disrespectful to your relationship. And if you live in the US then do yourself a favour and do not flush the fish because it is illegal to do so in the US!

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I would also recommend that you should give your fish a proper burial. You can put your fish from the plastic bag into a box or you can make a small cardboard coffin yourself and put your beloved fish in it. Here’s a video to help you out:

To bury your fish, just find a spot in your yard. To prevent your fish from being eaten by cats or dogs, dig at least 2 to 4 feet deep. Then just simply put your coffin in the hole you dug. You can also make a memorial and put it beside the burial site to honour your pet fish even more.

Other Causes of Fish Death

Here’s an interesting fact:

If you are wondering how your fish keep dying, then the cause might either be stress because of being bullied by other fish, being disturbed by loud noises or being disturbed by humans placing their hands in the fish tank.

Fish can also become stressed by the overcrowdedness of your fish tank so do not keep flooding your tank with more and more fish.

Other than that, here are some reasons why your fish might keep on dying:

1. Poor Water Quality: More the amount of ammonia in the water, the more unhabitable the water. Fish tank water gets polluted by rotting food and fish waste. You need to change the water regularly and avoid overfeeding your fish. Here’s a funny story from my childhood when I accidentally killed my first pet fish:

“I had bought a goldfish and kept it in a glass bowl. One day I was eating a banana and thought that I should feed my fish some banana too. So I put a small piece of banana in the glass bowl. After a while when I came to check on my fish, it had passed away.

I started crying at the poor sight but my elder brother, like always, was there to make it all worse. He took the glass bowl and ran outside while is chased him. He drained bowl beside the manhole at the end of the street.

My crying intensified and so did my brother’s laughter. But wait, it gets worse. Out of nowhere, a cat came, put the fish in its mouth and ran away.

I lost my voice and stood there looking at the spot where the dead body of my first ever pet was kidnapped by a hungry cat. From that day, whenever I ate a banana, I saw the face of my dear goldfish in front of my eyes.”

2. Insufficient Chemical Filtering: You need to filter the water every time you change the tank water and also use a dechlorinator.

3. Temperature of The Water: You need the keep the temperature of the water sufficient for the fish. The fish would get sick if the water is too cold. Similarly, the water must not be too warm either, because you are not boiling your pet fish to eat!

4. Contaminated Water: Water can get polluted by even a small amount of foreign material. So don’t make the mistake that I made and do not put even a little piece of banana in the water tank!

5. Illness: This one is a little difficult to handle as you might not know if your fish is ill or not. Also, before you treat the illness, you first need to know what type of disease your fish is suffering from.

Preventive and Protective Measures

Now you know the causes of death of your fish. But how do you prevent this from happening again?

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The first thing to do is to regularly observe your aquarium. Keep count of your fish and keep an eye out for anything out of the ordinary, especially with their fins. If the fins are ragged or the skin of one of your fish is scuffed, then that’s a sign that it is being bullied by the other fish.

Similarly, if their body is bloated then it’s an indication that there is an infection within the fish’s body.  If your fish is behaving strangely, this might mean that it is infected by a parasitic disease.

Change the water regularly and make it free of toxic and poisonous material. Keep doing water tests to know if there are any toxic material present or not.

If you’re unfamiliar with treating diseases in fish, consult a professional to get a proper diagnosis. Doing things on your own can often make matters worse in this situation.

Related Questions:

What type of household items can be bad for my tank water?

Anything from perfume, lotions, soap, and gasoline to scented spray devices, carpet or upholstery spray, sprayed glass cleaner and even concentrated cigarette smoke can be poisonous for your fish. These things should be kept away from your aquarium so your water does not get polluted.

How to sterilize your fish tank after a fish dies?

Firstly, remove the fish from the tank. Take everything out including the decorations. Now, use a cleaning solution made with 10 part water and 1 part bleach. You want to take an algae scrubbing pad and use this solution to thoroughly clean the interior and exterior glass walls of the aquarium.

Next, flush out all the solution to get rid of any remaining bleach. Then, clean out the filter. You need to use the bleach solution to clean as many filter components as you can. Once again, remembering to flush it all out thoroughly to get rid of any remaining bleach. Finally, clean all the decorations too and put them back in. While changing the water, you can add fish medicine to avoid the disease from coming back.

When can I put more fish in my tank after any deaths?

It depends on how your fish died. If everything seems okay with the other fish after you removed the dead fish, then you can restock within a week.

But it is advised to wait for full 7 days before putting any more fish in the tank. This is to detect if there is any problem with the fish or not. Do not keep adding more and more fish into your tank as it decreases the water quality.

Whenever you add new fish, observe all the fish and if there seems to be a problem, then do not add any more fish into the tank as it means that your aquarium is becoming overcrowded.

How do I know when a fish is about to die?

The fish becomes disoriented and may swim upside down. They leave food uneaten. Their gills become discoloured and white spots start appearing on their body or fins.

The fish would also have trouble breathing and would start gasping at the surface of the water. Other signs include mucus accumulation on the body and bulging eyes.


So, you’ve reached the end huh? I hope you that from now on you would not worry about your “fish situation” and take the precautions that will prevent more of your fish from dying. Just know that every life comes to an end and so someday your fish will not be with you. But you can always prevent any accidental death with proper precaution and care.

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Nadine Oraby

My name is Nadine; I am a passionate writer and a pet lover. People usually call me by the nickname “Joy” because they think that I am a positive and joyful person who is a child at heart. My love for animals triggered me to create this blog. Articles are written by vets, pet experts, and me. Thanks for visiting. Your friend, Nadine!

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