Can A Fish Drown (& How Can You Prevent It)

Looking at a fish it might seem safe to assume that they cannot be drowned. Fish sit every day of their lives in water without any problems, while humans can only survive a few short minutes at most underwater. In fact, a fish will suffocate if taken out of the water.

This ability to survive underwater when humans cannot has created many jokes and proverbs about how drowning a fish is impossible. This may not be true, however, since drowning is simply suffocating due to being under a liquid. If a fish cannot get what it needs from water for some reason, there is a chance it could drown. Based on our research fish may not be as immune to drowning as the old jokes and stories claim.


How do Fish Breath?

To understand how a fish might drown it is important to understand how fish breathe underwater in the first place. It should be said that fish do not breathe water itself and need oxygen just like most other animals. Instead of getting their oxygen from the air, however, they filter it out of the water.

Water has on average only 5% as much oxygen as air does, so fish need to very efficient in getting air out of water in order to survive. To do this they use their mouth and gills to constantly keep water pumping over the parts of their gills that absorb oxygen. This is why fish open their mouths regularly underwater.

Gill slits have a lot of surface area which lets them absorb more oxygen out of the water with each pump. This oxygen passes through the thin surface of the gills and into the fish’s bloodstream, since fish blood has less oxygen than the surrounding water and oxygen will always try to balance itself between two areas in a process called diffusion. From there the blood cells carry the oxygen where it needs to go in the fish’s body.

Fish also create carbon dioxide when they breathe which they need to remove from their bodies. Land animals do this by breathing carbon dioxide out between breathing air in. Fish do this by releasing carbon dioxide from their blood into the water as it passes over their gills. So gills both take in the oxygen fish need to breathe and let out the toxic carbon dioxide they need to release.

Fish also need special organs depending on what type of water they live in. Fish that live in salt water need ways to remove excess salt from their bodies so they can survive. Freshwater fish on the other hand need ways to keep as much salt as possible in their bodies.

Can Fish Drown?

Now that we understand how fish breathe we can understand how they can drown. Fish, like most animals, will drown if they cannot get the oxygen they need out of water, the difference is that fish have the ability to get oxygen out of water naturally. In order to drown a fish would either need to be in water with a low oxygen level or be unable to get oxygen out of the water around it.

It is rare in nature for a fish to drown since natural bodies of water tend to keep a steady supply of oxygen and have enough plants to absorb carbon dioxide without choking out any fish in the water. However, in a closed tank or aquarium there are a number of ways that a fish could drown if not properly taken care of.

One way a fish could be drowned in a tank is by getting pulled backwards through the water. Since getting pulled backwards would cause water to flow the wrong way across the fish’s gills it will not be able to get the oxygen it needs and it will die. Some fish can survive being pulled backwards but even then they may become exhausted from trying to escape whatever is pulling them back, causing them to drown as well.

Why do Fish Drown?

There are many ways a fish could drown in water which fall into two main categories. Either there is a problem with the fish’s gills or there is a problem with the water around the fish. Problems with a fish’s gills are often caused by the fish taking some kind of physical or chemical damage. Problems with the water around the fish have many causes and can mean the tank is not absorbing enough oxygen or that something else in the tank is using up the oxygen instead of the fish.

Problem with the Gills

One way a fish could drown is if their gills are damaged, since this would stop them from being able to filter oxygen out of water. A fish’s gills can be damaged in a number of ways, including attacks by other fish and chemical damage from products such as ammonia.

Some fish rely on ram ventilation, or swimming forward constantly in order to keep water flowing over their gills. If a fish that breathes in this way cannot move enough to breathe or becomes trapped it can suffocate.

While this is not a problem with the gills specifically, since fish breathe in oxygen and release carbon dioxide having too many fish in one tank can cause them to suffocate as they use up all the oxygen around them and fill the water with toxic carbon dioxide.

Problem with the Water

One common problem with the water in a fish tank or aquarium is not getting enough oxygen from the air. Bodies of water get oxygen from the air around them but since tanks and aquariums have less surface area they absorb less oxygen. This problem gets worse if the water is moving slowly or not moving at all since moving water absorbs more oxygen than standing water.

Temperature also plays a role in how much oxygen is found in water. The warmer water is the less oxygen it holds meaning that fish can drown in water if it is too hot and cannot hold enough oxygen for them.

Waste and plant matter in the water can also lower the level of oxygen in water, but for different reasons. If the water is full of waste it can reduce oxygen levels and even be toxic to fish. If the tank has too many plants, especially in a dark environment, the plants will use up the oxygen in the tank and suffocate the fish.

How to Stop Fish from Drowning

While fish can drown for many reasons there are also many ways to prevent fish from drowning by taking care of them and looking out for potential hazards. Make sure to research the fish and plants you put in your tanks so that you know what environment they need, how they interact with each other, and how to take care of them.

Fixing Gill Problems

The simplest way to protect the gills of your fish is to make sure you do not put too many fish into one tank and do not put fish that will attack each other in the same container. This prevents overcrowding from using up all the oxygen in the water and prevents fish from damaging each other’s gills.

Research the fish you buy to see if any breathe through ram ventilation. If they do take extra care to make sure they cannot get stuck in or caught on anything in the tank so that they do not suffocate.

When using chemicals like conditioners or cleaners on a fish tank or aquarium make sure you follow the instructions to the letter so that you do not leave dangerous residue behind that can damage the gills of your fish.

Fixing Water Problems

Tanks with more exposed surface area absorb more oxygen so having a larger or more open tank design can help the water exchange gas. Another way to increase the amount of oxygen in water is to install an air pump that moves water with less oxygen to the surface so that it can regain oxygen from the air.

Increasing the movement of the water has a similar effect to increasing the surface area. You can install devices such as spray bars, which spray water from aquarium filters back into the tank, and wavemakers, which generate fake ways on the surface of the water.

Since cold water absorbs more oxygen than warm water you should also keep an eye on the temperature of your tank or aquarium. Keep it out of direct sunlight and if you have a heater for the tank turn it off on particularly hot days. Be careful not to let the tank become too cold, however, or that could also be dangerous to your fish.

Make sure that you do not have too many plants in your tank so that they do not become overgrown. You should also watch out for green algae since it grows quickly and absorbs a lot of oxygen. Make sure that you do not leave the tank in a dark environment where the plants will start using up oxygen.


Based on our research fish can, in fact, drown in water if there is not enough oxygen in the water to sustain them. There are a number of ways a fish might drown including having its gills damaged, the water around it not absorbing enough oxygen, and other fish or plants using up too much oxygen in the water.

For this reason it is important to carefully manage your tanks and aquariums to make sure that the environment is safe for your fish.

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