Can Fish Drown in their Tank?

Fish will suffocate rather than drown. They don’t have lungs like we do. Humans drown when their lungs fill up with water. Fish can be starved of oxygen, which is different.

Like us, fish need oxygen to breathe.

how do fish breathe?
My artistic impression of how fish breathe.

Fish can’t breathe in air on their own, but they do have gills to extract oxygen from the water. The gills on a fish are their version of our lungs. Fish breathe by gulping in water, then their gills will extract the oxygen from the water, before it exits from the gill flaps, minus the oxygen, which is now travelling around the fish’s bloodstream.

This is all well and good until something happens to stop this process. In this case, they won’t get enough oxygen and can suffocate.

What Could Go Wrong?

Low Oxygen Levels in your Tank Water.

They are also at risk of suffocating if there are low levels of oxygen in your tank water.

If there are low levels of oxygen in the water due to a lack of aeration, fish will tend to gather at the surface and swim more slowly as they look for areas with higher oxygen levels.

To help prevent this, there are a number of things you can do.

The first, and most important thing is to make sure you have a water filter that is the right size and strength for your tank. This is essential as it is what keeps your water moving and aerated. Make sure you check it regularly and always keep your filter unclogged to make sure there is enough water circulation in the tank. Don’t clean your filter media (the spongy part) too often, or with clean water, as you will get rid of the good bacteria that lives in there which you need to keep your fish healthy.

Its pointless saving your fish from suffocating but then kill them due to an ammonia or nitrite spike because you are cleaning your filter sponge too much!

Adding live plants to your fish tank is always helpful. If you add live plants, they will absorb carbon dioxide from the water and release oxygen back into it.

If you don’t already have live plants, you will need to check that the fish you have in the tank aren’t tank reorganisers (step forward Cichlids…). Some species of Cichlids will dig them up just as soon as you put them in!

Not Enough Oxygen due to Overcrowding.

don't overstock your fish tank
Too many fish can spoil the tank.

This is a very common problem.

I speak from experience about this as it happened to me once.

I thought I had everything planned and went to my local aquarium with my water test results and the measurements of my tank as I knew it was dangerous to overstock.

Unfortunately, the aquarium decided to sell me too many fish, even though I had shown them all my measurements.

As a result of this, I lost 5 fish within a week, which was due to suffocation from having too many fish in the tank.

I now always check on a brilliant website called AQADVISOR. It is an aquarium stocking calculator where you add the measurements and water capacity of your tank, and then select some fish you are interested in keeping. The calculator will tell you what percentage full your tank will be.

It sounds awful, but I won’t be relying on a salesperson’s recommendations anymore as this calculator is spot on.

Debris Blockage in the Gills.

This can happen if your tank is dirty and doesn’t get regular water changes.

If your fish tank isn’t clean enough, particles of debris and waste will float around the aquarium.

As explained before, fish breathe by gulping in water through their mouth, which is then filtered through the gills to extract the oxygen. Debris from a dirty tank can become stuck in the gills and block them. This means the gills won’t work properly to be able to extract the oxygen that they need to live.

Gill Disease in Fish.

Gill disease is what can happen if you don’t maintain your tank properly.

Bacterial gill disease is a form of fish illness that often occurs when the living conditions are bad. This includes things like poor water quality, high organic debris and even increased temperatures in the tank. It can affect any size or age group, but usually it’s those who have weaker immune systems such as younger fish. Younger fish tend to be affected because they are more vulnerable to attack from pathogens found within these areas of concern.

Symptoms of Gill Disease include rapid or laboured breathing, swimming close to the surface of the water, and a lodd of appetite. The gills will sometimes be swollen or red, but it isn’t always clear to see this.

How to Tell if a Fish is Struggling to Breathe.

When a fish is struggling from lack of oxygen you will notice a change in it’s behaviour. Things like constantly floating at the top of your aquarium near to the surface or swimming upside down with its mouth open. Swimming becomes increasingly difficult for the fish as they get weaker, which will make them slow down. It will eventually be impossible for them to move at all.

It is more common for a fish to suffocate in a tank, rather than in their natural habitat because of the limited space.

In their natural habitats, They have so much more space, which means there is a higher level of dissolved oxygen and natural water movement to aerate the water they are living in.

If you undertake regular partial water changes, oxygen levels are replenished, as well as any dirt or debris being removed from the tank.

Most aquarium fish appreciate an air stone in their tank to help keep the oxygen level up as well as for additional aeration of the water. Some fish will actually play in the bubbles! Just be careful that you get one that is the correct size for your tank. If you get one that is too powerful, it will make the water too choppy for your fish, which will start to stress them out.

You should also check your air stone and airline every couple of months to make sure it is working properly, and that no debris is lodged and is causing a blockage.

Another instance where this might happen would be if someone overfeeds their fish, which could lead to the build up of toxins that would also kill them. This is one of the reasons why it’s important to monitor fish growth and only feed them what they need.

How to Help Prevent Fish from Suffocating in a Tank.

don't overfeed your fish
Don’t overfeed your fish.

To help prevent your fish from suffocating in a tank, you should always:

  • Clean out your filter and check to see it is working properly. You should only ‘clean’ your filter media with tank water as you want to keep the good bacteria that has formed on it.
  • Carry out regular water changes and vacuum your gravel to remove any debris that can start floating in your tank.
  • Increase tank size if possible to create more surface area, and don’t add any more fish.
  • Avoid overfeeding them or giving too many treats, which can lead to build up of toxins. If any food is visible after 5 minutes, you are feeding them too much, and it is best to try and remove the excess food where possible.
  • Add floating plants to the tank so they can use them as surface area (but not too many, because this will make it harder for oxygen to reach their gills)
  • If you already have living plants in your tank, don’t remove them all unless you are replacing them with more.
  • If you don’t have living plants, consider adding some if you have the space, and you don’t have any fish that are likely to disturb them.
  • Carry out a regular check on your heater and any air stone and airline you have to make sure they are working correctly.
  • Don’t overstock your tank. Use a stocking calculator to make sure you aren’t adding too many fish.

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