Fish Care

Can a fish drown in water? Find out here

can a fish drown

Can a fish drown? Not really, but they can suffocate in water.

Fish need oxygen levels in their home water to be two parts per million – or more – to survive. Without it, they become crowded (what some refer to as drowning).

What’s the difference here comes down to the meaning of the two words.

The Difference Between Drowning and suffocation

To say that a fish can drown is a bit misleading as the practice of drowning is described by the Oxford Dictionary as die through submersion in and inhalation of water. what does it mean to “drown.” When a human or an air breathing animal drowns, the water fills the required air gap. Eventually the animal is suffocated because the gases can no longer diffuse properly.

Fish do not have this issue because they use gills. Water can flow freely without interruption but still provides abundant supply of oxygen, carbon dioxide, ammonia, and other chemicals that can be exchanged with the environment.

Do Fish Need Oxygen to Breathe

To understand how oxygen levels in water affect fish, it is important to see how oxygen is transferred from the air to the water in the first place.

As human beings we need oxygen to breathe; the fish are no different. instead of taking in oxygen from the air like us, they accumulate oxygen dissolved in water while swimming.

There are more tons of oxygen in the air than in the water. This makes it easier to get oxygen when you live on land, but the fish have evolved gills to allow them to survive in the water.

Fish need oxygen for the same reason as humans do. Without it they will have difficulty breathing, and eventually, die.

How do Fish Breathe and Get Oxygen?

Fish do not have lungs like other animals. Instead, they have a gill. There is oxygen dissolved in water, but there is much less oxygen in the water than in the air, so fish gills need to work very well to absorb the available oxygen. The air contains about 210,000 parts in one million of oxygen and the water contains between four and eight parts per million oxygen.

How do gills work?

First the water needs to pass through it, which is controlled by the operculum (this is a skin layer that acts as a boundary between the mouth and the gills). The fish lower the floor of their mouth, this makes the pressure in the mouth lower than the external pressure, so water is drawn in.

When the fish lifts the floor of its mouth, the internal pressure exceeds that of the external one. This results in water coming out of the mouth through the operculum, and across the gills.

To extract oxygen from water, gills need more space. A large area means that as much water as possible can come in contact with the gills so that oxygen can diffuse across.

When water comes in contact with the gills oxygen is transferred from the water via the lamellae edge to the blood. Oxygenated blood is then pumped from the heart to the gills for gas exchange. Oxygen-rich blood is pushed from the glands to the rest of the body, without returning to the heart.

Why can fish can’t live outside the water since they use oxygen?

Fish will be able to have access to oxygen when they are out of the water, and at higher concentration. The answer is that they are not able to breathe, however, not because of the lack of oxygen.

Fish can’t breathe, because gills aren’t designed to process air, however, that doesn’t mean they can’t do it. The big problem is that the air dries them up. That is why they can no longer function properly.

Why would a fish suffocate?

If the water in which the fish lives in has a dissolved oxygen level of of two or less parts per million there is a high risk of the fish to be suffocated. This is unlikely to happen in the natural environment but in aquarium tanks it happens easily. This is why air pumps and filtration systems are needed in tanks to keep the water oxygenated.

What are the causes of Low Oxygen Levels in Fish Tank?

There are many reasons for low water oxygen levels, the most common causes being:

  • Overcrowding
  • Live plants (especially in cloudy dark tanks)
  • Low light levels
  • Excess waste
  • High water temperature
  • Certain chemicals

Low oxygen levels in the water are not the only reason fish can ‘drown’. Fish can have a problem which means they cannot process the available oxygen. If the environment is healthy and other fish are growing well, it could possibly be health issues.

There may be injuries or diseases affecting the gills that will impair the fish’s ability to breathe. Just as humans and mammals need healthy lungs to breathe properly, fish need healthy gills as well to breathe properly too. If a fish has a damaged gill, they have a high chance of suffocation, gill damage may be the result of predatory animal attacks or chemical damage.

Some species rely on regularly swimming forward to ensure that water passes over their gills, and if they stop swimming (for example, get stuck) or are dragged back they may suffocate.

How Do You Know If Oxygen Levels Are Low?

Fish living in areas where oxygen levels are low may show the following symptoms:

  • swimming around less
  • less eating
  • Spending more time around the surface and grasping
  • labored breathing
  • Rapid gill movement

The most common cause of low oxygen levels is overcrowding inside the tanks. Having too many fish in the aquarium is often the cause of the problem and has affected some of the above. As a result, overcrowding must be addressed to resolve the issue, otherwise the change you are making will only provide temporary relief.

How to improve oxygen levels in an aquarium

To combat the various causes of low oxygen levels, start by addressing the most common issue – overcrowded aquariums.

  1. Keep the right amount of fish

Every single fish you add to your aquarium results effect oxygen levels. Study the types of fish you have and the maximum per gallon. Make sure to aim lower than that number and definitely go with the lean side and also ensure proper cycling of your fish tank before you start adding fish to your tank.

  1. Maintaining proper oxygen

Another important factor in maintaining your aquarium with proper oxygen to ensure that there is enough space for gas exchange that takes place on the surface of the water. Instead of using small or tall aquariums, go for longer shapes such as traditional rectangles or bow shapes. a


Invest in other spray bars, aquarium bubbles, powerheads, or wavemakers to perform water-moving movements within the aquarium. Make sure you read the required flow of water for your specific species, however, to avoid overdoing it in the flow. Always ensure you keep your fish tank clean to keep your fish healthy and happy.

  1. Keep the right temperature in the aquarium 

Finally, keep your aquarium at the right temperature. Cold water naturally contains a lot of oxygen. Make sure you protect your aquarium from sunlight and go with the lower end of the temperature range for your fish.

Natural Causes of Low Oxygen Levels

Although very rare, there are cases where fish are suffocated due to the lack of oxygen in the environment as well. Some examples of this include:

  • Algae blooms – algae blooms can cause the amount of oxygen available to decrease. When algae die and decomposes this consumes dissolved oxygen and then decrease in available oxygen has a detrimental effect on aquatic life.
  • Decaying plants – immersed plants that die and rot can also contribute to low dissolved oxygen levels. The decay process is called Carbonaceous Biochemical Oxygen Demand (CBOD).
  • Chemical and crop runoff – flow from a variety of sources can cause changes in oxygen, nutrient levels and pollution in water which can also affect aquatic life.


So, there is it. Fish cannot really drown but can suffocate when the oxygen level is too low or if the fish cannot absorb oxygen properly from the water. But not because of submersion of water or inhalation, so they do not drown.

This is probably because people think that a fish cannot breathe and because a person can drown underwater is what they think happens to a fish that cannot breathe underwater.

In both cases, they both have respiratory tract. Lungs and Gills are designed for use in air or water, and are more efficient in their natural environment than in any other habitat.

Having look at the word drown; you can see that fish do not die by inhalation of water. So, while fish may not drown, they may go through a similar experience when they come out of oxygen or water.