Can A Fish Drown: A Common Misconception

Can a fish drown | Fishkeeping Adventure

Drowning is an action where a living being who thrives on air runs out of it due to water flowing in. This is not to be mistaken for suffocating which only refers to a cut-off in air supply.

So, if aquatic creatures live in the sea for all of their lifetimes, can they experience drowning? Can a fish drown when it is always submerged in water?

It is a very popular misconception that a fish can’t drown since it already lives in the water. Take note, the definition of drowning involves ‘running out of air.’

And since fish needs air, specifically the oxygen component, if it runs out of it and the surrounding water fills up that void, then a fish can, in fact, drown and die.

How Can A Fish Drown?

You may be wondering; how can a fish drown in water when it has naturally learned how to live in such an environment? Before we can identify the situations where a fish can drown, let us understand first how fishes breathe.

How Does A Fish Breathe?

First and foremost, we need to state the obvious: a fish needs oxygen. Without it, a fish can suffocate or drown. How does a fish breathe? Does it have a nose?

Like any other vertebrate animal, fishes have brains, hearts, muscles, tissues, and other essential inner organs such liver and kidneys. The blood cells, which make the aforementioned body parts function, need oxygen.

To gather oxygen, fishes have “gills” in replacement for a typical respiratory system.

Role Of Oxygen In A Fish’s Body

Organs like the heart, brain, liver and kidneys work similarly to other vertebrates. Oxygen is pumped into the blood and the cells keep on working as long as the organs still exist.

Other organs are unique only for fishes and one of them is the “swim bladder”.

The swim bladder’s purpose is to help a fish control its position in the water. It is filled with gas that will maintain the fish’s body’s neutral buoyancy and keep its position in the water.

Although most fishes have swim bladders, some that don’t will have to rely on swimming momentum to keep upright. 

The other unique organ is the “gills”. As mentioned, fishes don’t have the typical respiratory system which is comprised of the nostrils and the lungs.

Gills take the role of it. This is possible mainly due to the group of cells called “epithelium”.

When water moves across the epithelium’s membrane, the oxygen content in the water is dissolved and absorbed by the fish’s veins. Next, the arteries will deliver deoxygenated blood to the epithelium and the cycle continues on and on.

Similar to other vertebrates, the by-product of the fish’s cell respiration is carbon dioxide.

Effect Of Oxygen Intake On The Evolution Of Fishes

Due to being in the water all of the time, fishes rely on their gills to breathe oxygen. They have relied on them so much that they cannot breathe properly when taken out from the water.

This is because of the gills’ unique aspects.

Fishes push water towards their gills by spreading their skin flaps around that area. This is similar to how humans, who are naturally living on land only, use nose to breathe.

In other words, gills cannot work well without water. Therefore, a fish cannot obtain the needed amount of oxygen if exposed outside the water’s surface.

When a fish finishes utilizing the water for oxygen content, it is expelled out through an opening known as the “operculum”.

To land-dwelling and air-travelling vertebrates, the process of how fish breathes is nearly impossible to comprehend.

In comparison, the amount of oxygen in the air is 210,000 parts per million while in water, oxygen is just 4-8 parts per million. This means that breathing underwater is very difficult and tasking.

The reason why fishes find it easy is because, throughout millions of years, they have adapted to such a process.

In fact, fishes are considered ‘cold-blooded’ animals because they need lesser amounts of oxygen compared to non-aquatic animals. This is the magnificence of what evolution can bring out.

What Are The Reasons For A Fish To Get Drowned?

After learning how fishes breathe, we will address the question of whether a fish can drown in a detailed manner. For starters, the only way a fish can drown is to deprive it of oxygen.

Once there is a lack of oxygen, blood cannot flow well, and it will result in multiple organ failures.

In that case, the oxygen content of the water is the key to how well can a fish breathe. For fishes, the critical amount of oxygen absorbed is anything below 2 parts per million.

What can be the possible reasons why a body of water arrives in such an unfavorable situation? The list below will uncover them.

1. Overcrowding

Let’s say that a single tree can provide 10 humans with the optimal amount of oxygen needed. If those humans started to expand while no additional trees are planted, the amount of oxygen received by each one will definitely be lesser.

That is also true for the fishes. If you pack many of them inside an aquarium, even if they are peaceful with each other and being fed on schedule, a number of them will slowly die.

That is because the oxygen content of the water inside the tank is simply not enough to accommodate the growing demands.


If you are planning to have a fish tank, research first the optimal needs of your chosen fish. The greater the volume of water, the better it is for them.

However, you might have budget constraints so it’s highly recommended to consider the largest minimum tank size among your chosen fishes.

2. Insufficient Water Surface Area

Let’s say you transfer your growing fish to a larger container after realizing its growth spurt is a problem. You may get complacent and might start to add decorations to make the aquarium’s appearance better.

Little did you know that by doing such, you have reduced the water surface area and that can affect the interaction of water with the atmospheric air.

Furthermore, as the fish breathes oxygen, carbon dioxide is expelled into the air. If the water surface is reduced, assuming your fish tank doesn’t have a water pump for circulation or a breather apparatus, oxygen from the atmosphere can’t enter the water and will leave the fish to breathe its carbon dioxide.


If you prefer to build an enclosed fish tank, make sure you have a breathing apparatus for the circulation of oxygen. If you prefer simple solutions, then research your fish’s tank size requirements, provide a container of such size and make sure not to cover the opening.

3. Algae Blooms

If you are not familiar with algae, it is an organism that resides predominantly in water. They are plant-like species even though they lack common characteristics like roots, stems and leaves.

They are considered such because they thrive on photosynthesis, which is a process unique to plants wherein the energy of the sun is absorbed to generate their food.

Although it is only natural for algae to exist in aquariums and ponds, the term ‘algae bloom’ refers to the rapid increase of the specie’s population. This increase results in the expansion of the territory of the bacteria residing on it.

Therefore, if there is an algae bloom, there will be more bacteria that can deplete the oxygen content of the affected area.

How can such a scenario occur? One common reason for an algae bloom is excessive nutrients in the water content. This means that there are many leftovers in the aquarium or pond.

This is not to be confused with the presence of feces or vomit.


If the water turns green, that means that there is an algae bloom. You can solve such a problem by replacing the water content with a cleaner batch. Even better if you can prevent algae blooms by not overfeeding your fish in the first place.  

4. Soaring Water Temperatures

The reason why information about fishes always includes the ideal temperature of their water is to emphasize the importance of maintaining the actual temperature of your aquarium or pond within that range only. If not, there will be unwanted consequences.

Much like the land-dwellers, fishes can also suffer from excess heat. When water gets warmer, it will hold less dissolved oxygen.

This means that the gills will have difficulty complying with the fish’s oxygen requirement. Furthermore, the increase in temperature can alter the water chemistry.


For aquariums, you can provide cooling devices. A cheaper solution is to place them wherein they are not under direct sunlight.

For ponds, you can add shade nearby. They can be covers or potted plants that can cast large shadows on the pond’s water surface.

5. Inadequate Water Movement

Oxygen from the atmosphere needs to flow in and carbon dioxide must flow out. In that way, fishes can continue to have an oxygen supply within the water and won’t have to breathe in the harmful carbon dioxide.

However, there can be situations when you can’t gauge if the tank is overpopulated or if its opening is adequate. Furthermore, it’s unrealistic to spend all of your time just monitoring the tank’s water temperature.

The key to reducing future unwanted problems from these possible situations is the tank’s water movement.

Under those aforementioned circumstances, if the water remains stagnant, it will automatically spell doom.

Algae blooms can occur, and fecal matter might not be filtered well. With a constant flow of water, the tank is replenished, and it can mitigate the problems like rising temperature and lack of new sources of oxygen.


Having an additional pump or replacing the current one with a more powerful type can make the water flow better. Having a great water movement inside the fish tank can generally solve almost all of the problems listed in the list.

However, certain fishes are sensitive to the changes in the environment and better water movement might not be enough.

6. Lack Of Plant Life And Lighting

As we all know, plants provide oxygen in exchange for carbon dioxide. They are the perfect complement to all humans and animals since we need oxygen, and we give off carbon dioxide.

Because fishes need to breathe properly, it will be beneficial to add some plants to the fish tanks.

But the question is can any plant be put inside the tank? A portion of your succulents or stems from potted plants don’t count since they don’t survive in the water.

They will be just as useless as the floating wooden branches. If you are looking to add plant life to your fish tank, choose aquatic plants.

Moreover, adding plant life to the tank is not enough. You need to make them sustainable and beneficial to the enclosed ecosystem.

Plants need sunlight since they rely on photosynthesis to survive. The only way to achieve that is to provide enough lighting for your tank.


For options on aquatic plants, you can refer to your local aquarium store. For outside ponds, lilies are the most common choice.

If your aquarium happens to be in direct contact with sunlight, you can add many aquatic plants. If your tank is located in a very shaded area, you need a very luminescent lamp.

7. Excessive Plant And Animal Waste

Adding aquatic plants is very beneficial to the fish inside the tank. However, there will come a time that they can become detrimental too.

If plants start to decompose due to being eaten by the aquatic creatures, they are as bad as debris or waste. They may not be that harmful, but they can form a cluster with the more problematic algae blooms.

Another type of waste that contributes to the oxygen problem in a fish tank is animal waste. Fishes urinate and defecate within the very waters they swim.

If the water content has more fecal matter, there will be lesser room for oxygen to consume. Take note, animal waste can be denser than water and after a few hours, it can settle at the bottom if not cleaned.


Plant debris can be obtained through a net. For animal waste, the movement of the water and the quality of the filters can be enough.

If you add waste-consuming fishes like the janitor fish, make sure that there are no smaller fishes that can become their prey.

You can also try using a gravel vacuum to remove waste that has settled at the bottom of the tank. If the water is too polluted, replacing new water is a must.

8. Parasites And Diseases

Contaminated water can bring a lot of problems if not attended to. Undesirable microorganisms can spread in numbers which will, sooner or later, cause sickness to the fishes.

These creatures exist due to the presence of too much waste, the decomposition of a deceased fish or contact from foreign bodies with the fish tank’s water.

Parasites like flatworms and gill fluke affect the fish gills. These can cause inflammation and encourage the affected fish to scratch the gills it finds irritating on hard surfaces.

Worse, the gills might get damaged and automatically cause difficulties in breathing. Since the invading species are parasites, fishes might also lose their appetite for food.

Another bothersome situation for the fish is having to deal with fungal and bacterial infections. Some of the common infections are bacterial gill disease and amoebic gill disease.

As the population of bacteria and fungi grows inside the fishes, they will have more demand on oxygen to survive. If not treated immediately, they will drown apparently.


The growth of undesirable microorganisms can be avoided by maintaining the cleanliness of the water. This involves good water movement and an acceptable temperature level.

If the fishes happen to suffer from diseases because of parasites and bacteria, it is urgent to isolate them from the unaffected ones for treatment.

9. Chemical Treatments

Oxygen levels within the fish tank can change because of the presence of chemicals. If you are wondering what the chemicals are, they can be any liquid being put in the tank that is not water.

Some fish medications can be liquid and contain chemicals that might change the water’s acidity.

Some of them can also be solids. Together with the food pellets, if they are not consumed, they will break down and be mixed in the water.

Ammonia can build up and affect any fish in contact with it. Although not necessarily harmful to humans and other larger vertebrates, fishes are sensitive to ammonia.

Their gills can bleed, and more oxygen would be needed to cope.


The only thing you can do to counteract the negative effects of the chemicals inside the water tank is to increase the flow of water. With this, clean water can be replenished, and the contamination can be filtered out.

10. Body Modifications

There are special types of fish that can survive with low oxygen levels in the water and have the ability to breathe from atmospheric air once they emerge at the water’s surface. These are the lungfishes and the labyrinth fishes.

While lungfish are rare, labyrinth fishes can be common and work well inside the water tank ecosystem.

One common example of labyrinth fish is the betta fish. The labyrinth organ is responsible for its very unique trait.

Because of that, many breeders throughout the years have sought to create breeds of betta fishes.

Unfortunately, such action has backfired since some betta fishes have longer tails. Can a fish drown from that? Yes, of course.

The tail growth puts that type of fish struggle in swimming toward the water surface to gasp for air. If succumbing to such difficulty, the betta fish can drown.


If you are keen on growing the aforementioned type of fish, it is important to do a bit more extensive research. Even better if you can consult a much more experienced breeder or pet owner.

Frequently Asked Questions

Q: Can You Suffocate A Fish In Water?

A: Technically, suffocating is the more appropriate term than drowning since a fish doesn’t inhale water. When the gills get damaged, the oxygen supply is affected and might be cut off, hence the suffocation.

If the fish struggles, water can flow through the mouth or other openings and the fish will die from drowning. It only takes 3 to 4 minutes without any gill movement for a fish can lose its life.

Q: What Kind Of Fish Can Drown?

A: All fishes can drown including the lungfish and labyrinth fish. As long as there is no oxygen intake, after a while, the fish can die.

Q: Can Fishes Feel Pain?

A: If you think about it, there are many organs a fish has that are similar to humans. If we feel pain when those organs get damaged, fishes also have the same capability.

We only view them as negligible since the pain indicators for fishes look meaningless to us.

Q: How Do Fish Pee?

A: Fishes pee based on the capacity of their kidneys. Some species have a smaller capacity while others have a longer capacity and can last days without urinating.

It will seem to us that fishes don’t pee but in reality, they do. However, it can take a long while due to the pace of their food digestion.

Q: What Happens If You Put A Fish In Milk?

A: Can a fish drown in milk? First of all, it will have a rough time surviving due to the chemical content and presence of substances that can deteriorate its gill’s function.

If it will have difficulty living, naturally it can easily die.


A fish can drown in water. As long as the oxygen level of the tank’s water is below the critical level, it can die from drowning. There is only one main solution to such a problem and that is to prevent the reasons mentioned above from occurring. Let nature takes its course and as humans, we don’t have to interfere.


Edwin is a passionate fishkeeper since he was a kid. He loves caring for the fish and sharing his ideas about fishkeeping with family and friends. He is the owner of Fishkeeping Adventure.

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