Can Fish Drown? Is It Possible?

Estimated read time 16 min read

In this article, you’ll learn if it’s even possible for a fish to drown in water.

We’ll also explain how fish breathe, signs of low oxygen, how their gills work, and lastly, what you can do to ensure your fish always have enough oxygen.


Equipment To Help Oxygenate Your Aquarium

Do Fish Need Oxygen

A common misunderstanding among people is that fish don’t need to breathe air. This could not be farther from the truth.

Like humans, all species of fish need oxygen to breathe. A lack of oxygen can be fatal for fish.

Next, let’s explain how fish breathe while underwater.

How Do Fish Breathe and Get Oxygen From The Water?

Basic high school science teaches us that plants give off oxygen through a process called photosynthesis.

So how do you get dissolved oxygen in water?

Well, live plants may be the most significant oxygen source, but they’re not the only ones.

While they aren’t technically plants, Algae also produces oxygen in the water, as do other organisms like blue-green bacteria.

Fish get their oxygen from the water and absorb it through their gills’ delicate blood vessels. And while fish get most of their oxygen through their gills, a small amount also passes through their skin.

So, the greater the surface area, the easier it is for fish to absorb oxygen.

The oxygen travels through the fish’s body and seeps into all the areas with a high amount of carbon dioxide.

Then the fish’s gills release the carbon dioxide, similar to how humans exhale carbon dioxide when breathing.

When water oxygen levels are low, fish shift to anaerobic respiration, but they can only sustain this for a short period.

Signs of Low Oxygen

Fish need oxygen to survive.

So how can you tell if your fish tank has low oxygen levels?

Testing the water concentrations regularly is the best method of ensuring a significant amount of oxygen in the fish tank.

But the attentive fish keeper will also tell whether there is enough oxygen in the water from how the fish behave.

If your fish cannot breathe, there will be small and gradual changes to their behavior patterns.

Here are a few signs;

Your fish may become lethargic. Their movements will become slow, and their appetite will decrease.

You’ll notice fish food collected at the bottom of the tank, and your fish will stop swimming forward at the prospect of food.

Catching the problem at this stage is the best-case scenario because it’s easily solvable.

But what happens if the issue remains unaddressed?

When your fish tank’s oxygen levels fall to distressing amounts, your fish will start panicking.

Unable to get oxygen, fish may dart and gasp at the surface of the water. You’ll also see them rapidly flapping their gills as they try to get enough oxygen and save themselves from drowning.

These are all incredibly worrying signs.

Remember, your fish can suffocate, and if you see them gasping at the surface of the water, darting out of the tank, that’s a code red.

However, if you own labyrinth fish like betta fish or gouramis, you’ll notice them regularly swim to the surface of the water and casually pop their head out of the fish tank and dart back in.

This is routine behavior for these fish species and isn’t characterized by panicked gasping, continuous open-mouthed sucking at the surface of the water, or rapidly beating gills.

What Causes Low Oxygen Levels?

Knowing how to identify low oxygen levels is essential because you can still act fast, take the proper emergency steps and save your fish.

But what’s more responsible is learning what causes low oxygen levels in the water so you can avoid the crisis altogether.

  1. Overcrowding is the most significant cause of oxygen depletion. If there are too many fish in a small tank, there won’t be enough oxygen in the water. And fish can drown in circumstances like these.
  2. Lack of water movement can also reduce the amount of dissolved oxygen. When the water isn’t properly circulating in your fish tank, you’ll have oxygen in the water at the top surface, but the fish at the bottom of the tank won’t get the oxygen. A fully functioning filter helps encourage water movement, so there’s an equal amount of oxygen throughout.
  3. Low maintenance and irregular cleaning of the fish tank can remove oxygen from water. That’s because fish poop and overgrown algae can clog filters. Other than that, when you leave excrement in your fish tank for long periods, the bacteria in the body of water will start using the dissolved oxygen to decompose it.
  4. Cold water holds more dissolved oxygen than warm water, so when you’re changing the water in your fish tank, low-temperature water is the better option. That said, you need to meet the fish’s ideal temperature range, and that value changes from species to species. If your tank overheats, remove the cover and turn off the heater and lights. Use a fan to blow cool air near the surface.

Can There Be Too Much Oxygen in the Water?

Can a fish drown in water?


But what about the opposite?

Is there such a thing as too much oxygen?

The oxygen requirements for fish vary depending on their species.

The lowest oxygen level for Lake Trout is 8.3 ppm, while that for Carp or Bullheads is 4.0ppm.

Overall, the dissolved oxygen content should not cross 110 percent.

Can fish drown if the dissolved oxygen levels are too high?

Definitely, it’s called “gas bubble disease.”

When there’s excess air, it enters the fish’s gills and can form air bubbles that block blood flow. Fish can die if this happens.

On the other hand, levels below four ppm are harmful to fish and can drown fish.

So the best strategy is to look up the specific oxygen requirements for your fish species and use a dissolved oxygen meter to keep track of the oxygen level.

How Do Fish Gills And Their Other Organs Work

Fish cannot take in oxygen from the air. Aquatic respiration works a lot differently.

So the gills are placed on either side of their body next to the fish’s head. When a fish opens its mouth, it may appear as though it is trying to breathe as humans do, but that’s not the case.

Instead, that motion causes the water to run over its gills and contact dozens of capillaries.

These capillaries absorb dissolved oxygen. And that’s how fish absorb oxygenated water through their gills.

Next, the blood vessels transfer the oxygen to all the fish’s body parts and replace the carbon dioxide.

Eventually, the carbon dioxide goes back to the gills and is removed.

In many ways, there are huge similarities with the human respiratory system in how both gases are absorbed and removed.

The gills are a sensitive barrier, and the high surface area of the thin epithelium layer helps maximize the rate of oxygen absorption.

Since a fish’s gills are essential to its respiratory processes, a bony plate protects the gills. The plate or operculum opens and closes as needed.

Do Fish Have Lungs?

Fish do not have lungs as humans do. Instead, it is the gills that perform all the respiratory activities.

When fish take a huge gulp, their mouths fill with water. This water then passes through the gills, where the filaments absorb the oxygen.

The gills remove the oxygen from the water, absorb it into the bloodstream, and then circulate it to the heart.

Later, moving through the heart to all the other parts of the fish’s body, specifically those organs with less oxygen.

What Are Labyrinth Organs?

One exception to this process is the Labyrinth fish which has a unique makeup that sets it apart from other fish species.

The reason is the labyrinth organ can absorb oxygen from the air.

The fact that these fish can air-breathing makes them uniquely suited to surviving in low oxygen water bodies.

Additionally, these fish are born with a fully developed labyrinth organ.

However, one side effect of this evolved respiratory system is that these fish can’t survive simply through the inhalation of water. They need to dart to the surface and breathe air to survive.

Some famous examples of fish that have a labyrinth organ are the Betta Fish & Gourami.

Drowning Fish

Now that we know fish need oxygen to survive and that they can die from lack of it, the question becomes not “can fish drown” but rather “how can fish drown?”

How Does A Fish Drown?

The sole purpose of the gills is to absorb dissolved oxygen from the water. So when there is less oxygen in the tank than needed, the fish can suffocate and drown.

How does this happen?

Since almost all fish are cold-blooded, they require lower amounts of oxygen than warm-blooded mammals.

They can typically get this amount from water, but if the oxygen levels in your tank fall below the required amount, they will drown.

Can Fish Drown Underwater?

The average oxygen requirement for fish is 4 to 8ppm, so if your tank’s oxygen levels fall below that level, the fish will not get enough oxygen.

Its organs will start shutting down, and eventually, there will be no oxygenated blood to reach its heart.

And we all know what that means.

Do Fish Drown In Air?

Fish can also drown in the air simply because they can’t draw oxygen from the air.

So as far as they are concerned, there is no available oxygen for them to breathe.

Eventually, they will suffocate and die.

Fish Suffocating

As a fish owner, you’ll often hear people say their fish “drowned.”

While it is a part of the commonly used lexicon, it is technically correct to call this phenomenon “drowning.”

Can Fish Suffocate?

When fish “drown,” it’s because they couldn’t get enough oxygen.

That can mean there wasn’t enough oxygen in the water, the air pumps weren’t working, the oxygen wasn’t circulating, or the fishes’ gills were damaged.

While there is a multitude of reasons, the result is the same.

That’s right. Your fish can suffocate when they don’t get enough oxygen to function.

Eventually, their organs start shutting down, and they die.

Yes, you can call this drowning since that’s socially accepted lingo in “fish circles,” but it’s suffocating.

Do Fish Suffocate Out Of Water?

Similarly, when fish die out of water because they can’t absorb or process the oxygen in the air, that is also suffocation.

Again as we discussed earlier, you can also say that “fish drown in the air,” but it is just an issue of semantics.

We use the term drown with regard to water because humans drown in water when they don’t get enough oxygen.

However, dying because of a lack of oxygen is also termed suffocating.

It’s a sentimental topic of discussion. And not one I’d recommend you bring up at dinner.

But you get the idea.

Tips To Keep Your Fish Breathing Easy & Improve Oxygen Levels In Your Aquarium

Now that you know what the potential issues are, the question becomes;

How can you avoid it all? And What can you do to keep your fish healthy?

As a beginner fish keeper, it is essential to read up on what mistakes you should avoid.

After all, there’s a learning curve to most tasks, but you don’t want to fall too far behind and risk killing your fish.

Below are a few tips to help ensure your fish get enough oxygen.

1. Don’t Stock Too Many Fish.

Stocking too many fish is the first mistake you can make and a common one among people starting.

Think of it in human terms.

If ten people are stuck on a small elevator eventually, the air will run out of oxygen, and you’ll find it hard to breathe.

Similarly, if you keep too many fish in a small aquarium, they won’t have enough oxygen to meet their needs.

Does the question then becomes;

  • How many fish is too many?
  • Is your tank suitable for three fish or five or eight?
  • What about a fishbowl?
  • Can you keep more than one fish in it?
  • And is three too many?

The only person who can answer these questions is you. You’ll need to do some research.

But if there is one tip I can give you, it’s this;

Don’t try to save money by buying a smaller aquarium than recommended.

Bigger, in most cases, is most certainly better!

And if you’re getting more fish, find out whether your old tank is suitable for the larger number because you may need to get a bigger one.

2. Increase Water Surface Area

We’ve discussed the gas exchanges that occur within the tank and amongst the fish.

But what about the surface of the tank itself?

The oxygen in the air diffuses into the water at the surface. That’s why you need to purchase items like air pumps, air stones, and recirculation pumps and filters.

These pieces of equipment do a great job at moving the water and agitation the water surface.

So when you’re buying a tank, it’s a good idea to get one with a larger water surface area and maybe don’t use a lid.

Doing this allows the largest water surface to be in contact with the air.

And, of course, you’ll need other processes for water changes and circulation to set up a viable fish habitat.

3. Keep Your Water Moving

Since the oxygen collects at the surface, it is essential to keep it moving. That way, you get aeration throughout the aquarium, and the fish at the bottom of the tank can breathe.

One way to ensure this is to invest in quality equipment like spray bars, powerheads, and aquarium bubblers.

This is especially important for fish species that absorb oxygen through the gills by swimming forward.

However, keep in mind not to overdo the currents.

4. Watch Your Water Temperature

Warm water does not contain as much oxygen as cooler water. That’s because the water molecules are moving faster.

As a result of this increased movement, more significant amounts of oxygen are released, and very little remains dissolved.

So it’s in your best interest to keep your fish tank temperature consistent and controlled in the lower range.

Additionally, warm water is a double-edged sword.

Fish digest their food slowly in cold water because their stomach enzymes are relatively inactive. These processes speed up exponentially in warm water because the higher temperature makes the enzymes work in double time.

Fish will also eat more and swim around in their tank. All of this requires energy and oxygen.

The warmer the water temperature, the more oxygen your fish will require to survive daily.

So they need more water than usual, but they’re getting less than they would with cooler water.

This makes for a dangerous situation.

That said, you don’t want to overcorrect and expose your fish to freezing temperatures.

Too low, and your fish will become sluggish. While the specifics depend on your fish species, the 65-70F range works for most aquariums.


How Long Can Fish Breathe Out Of Water?

Most fish cannot survive on land for very long. Pet fish are incredibly delicate in this regard.

The average time your fish could survive out of water is no longer than 10 minutes. And this is a loose estimate.

The specifics would depend on fish species, size, natural habitat, and other health conditions.

Overall, if you’re considering keeping your fish out of the water while cleaning your tank or replacing the water, we would strongly caution you against the idea.

Even if your fish can survive the short period, you’ll stress it out, and it may die in the hours or days after.

Why Don’t Fish Fill Up With Water?

Fish are unable to store water and cannot fill up with water.

It is the process of taking in water and expelling it through the gills that allows them to extract oxygen.

Additionally, there are also other factors to consider, like the saltwater balance.

Freshwater fish require low quantities of salt to survive and pee out excess water to avoid overhydration.

On the flip side, saltwater fish excrete salt to retain the small amount of water they need to survive.

These self-sustaining systems allow fish to maintain their ideal internal systems.

Can You Drown A Fish By Pulling It Backwards?

We’ve discussed how fish absorb dissolved oxygen by swimming forward. It is this frontward motion that lets the gills take in the required amounts of oxygen.

So you may find yourself wondering what happens if a fish is pulled in the other direction.

This backward motion will drown the fish because it will not be able to get the needed oxygen. The gills aren’t designed to work that way, and you could cause permanent harm to your pet, if not death.

Can A Betta Fish Drown Even Though They Breath Air?

A few species, such as betta fish, can extract oxygen from air using what experts term the labyrinth organ.

So they can swim to the surface to take a deep gasp of air and always stay underwater to let their gills do all the work.

This begs the question, do they need both methods, or can one sustain them?

Betta fish and other labyrinth fish still require both methods to breathe.

For example;

When there is very little oxygen left in the water, the betta fish swims to the surface to get oxygen from the air, but they still require water in this process.

However, if a betta fish is weighed down or can’t reach the top of the tank, it will drown.


If the oxygen is depleted or doesn’t circulate and reach your betta fish, then it will drown.

Why wouldn’t a Betta be able to reach the water surface?

Because of unethical practices, such as overbreeding to create large or oversized tails and fins.

These genetic modifications can weigh them down, and if a betta fish cannot swim to the surface of the water, it will drown.


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