🐠 Can Fish Drown?

Yes, it is possible that a fish can drown. The reason for drowning might be the suffocation caused due to low dissolved oxygen, the temperature of the water, overcrowding of living species, or the impurities present in the water. Well if you are wondering about the sinking of fish in the water, then the answer is no because the density of fish is similar to the water and they have the ability to regulate their average density to swim at different depths without spending much energy.

Image Source: Ajale, Pixabay

What is drowning for fish?

Well to answer this question we need to understand the meaning of ‘drown’ because our answer might vary with the definition of it.

According to the Cambridge dictionary, the definition of drown means

“To (cause to) die by being unable to breathe underwater”

As per the above definition, fish can drown because there can be several reasons such as contaminated water and low oxygen level in the water which can cause fish to die.

If you look at the other definition of drown:

“The death caused due to suffocation when water or other liquid fills the lungs”.

Well, according to this definition, it is technically impossible for fish to die because they don’t have lungs for breathing but we know that they can suffocate underwater. This definition holds true for humans because we have lungs and if our lungs get filled with water, we can suffocate and die.

Read: Do fish have teeth?

Is it possible to drown a fish?

The answer is yes, fish can drown underwater by getting suffocated. Similar to humans, fish also cannot survive without oxygen. Oxygen plays important role in producing energy which is essential for the metabolism in living organisms. Therefore, if fish is exposed to some alien environment for which it is not evolved, it will surely die because of suffocation. For example, we know that fish cannot survive in the air even though the air has enough oxygen. This is because fish don’t have lungs like humans do and thus, not adapted to survive in air. Humans do have lungs to breathe and survive in air. However, they can drown in water because our respiratory system is not made to survive underwater.

You will be surprised to know that freshwater fish also might find it difficult to survive in salty water and vice versa. In these cases, the tonicity of water affects the survival of the fish.

Let’s understand how fish breathe underwater or take oxygen into the body.

We know that fish don’t have lungs like human do but they have gills which help them to breathe and absorb oxygen from the surrounding water. The surrounding water enters into the mouth and then passes through the filaments of gills. The oxygen in the water gets absorbed through the network of capillaries present in the filaments. Simultaneously, the waste such as carbon dioxide gets dissolved in this water.  Then this water with waste products exits the fish body through the gills flaps.

Read: Do Fish Have Tongues?

From the above breathing process of fish, we can infer that the surrounding water plays important role in the survival of the fish. Contamination of this surrounding water can result in the suffocation of fish.

There might be several reasons for contamination in water that might cause fish to suffocated and die such as

  1. Amount of Dissolved Oxygen: Dissolved oxygen refers to the concentration level of oxygen present in the water. Low dissolved oxygen water can cause breathing difficulties for the fish. The oxygen holding capacity of the groundwater is naturally low as compared to the surface water which is exposed to the atmosphere because the dissolved oxygen mainly gets absorbed into the water from the atmosphere.
  2. Tonicity of Water: Tonicity is the relative concentration of solutes dissolved in the water which drives the direction and extent of diffusion. This is the reason why saltwater fish cannot survive in the freshwater and vice versa. Saltwater fish in saltwater has to intake a lot of water because the concentration of solute in the surrounding water is more than the solute present in the body and the body is naturally losing water to the surrounding. Therefore, when a saltwater fish is exposed to the freshwater, it will get swollen and die because freshwater has low solute concentration due to which the body will not lose water naturally. On other hand, freshwater fish has not evolved to intake more water as the surrounding concentration of solute is low. Therefore, if we put freshwater fish in salty water, it might die because of dehydration.
  3. Overcrowding of living species: If the water reservoir is overcrowded with a lot of living species, in that case also fish might die due to suffocation. This is because more the species, more dissolved oxygen will get consumed. If the rate of consumption is more than the rate of absorption of dissolved oxygen in the reservoir water, then sufficient oxygen is not available for all living organisms. Therefore, if you have a fish tank, always make sure it is not crowded.
  4. Water temperature: The oxygen holding capacity of water decreases with the rise in temperature of the water. In warmer water, the oxygen solubility decreases, and metabolic rates increase that affects the respiration in fish. Therefore, always try to maintain the temperature in the fish tank.
  5. Impurities in Water: The water contaminated with soluble minerals and other chemicals can also cause suffocation for fish. The presence of these substances reduces the amount of oxygen in the water that causes fish to drown. This is the reason why fish cannot survive in milk, beer, vodka, and other liquids.

Read: Can a fish drown in milk?

Can fish drown if they stop swimming?

Well it is an interesting question and you are referring to sinking of fish in the water.

The answer to this question depends on the density of fish as compared to water.

Fish cannot drown if they stop swimming because the density of the fish is usually the same as the density of the surrounding water in which it swims. Most of the fish have a swim bladder (also known as gas bladder filled with oxygen) which helps to regulate the density of the fish. With the help of this bladder, fish changes its average density to float at different depths without putting much effort.  

Even when the fish die, they cannot drown because the body of fish gets swollen due to the gases produced during the decomposition by bacteria. Hence, the density of fish decreases and it floats on the water.

Read: How Do Fish Taste?

How long does it take a fish to drown?

Time taken by fish to drown depends on the surrounding conditions of the fish.  Here are few scenarios:

If fish is exposed to air, it may take few minutes (three to four minutes) to die.

If fish is exposed to water with low dissolved oxygen, then they may last from few days to few months depending up on the oxygen concentration level.

If the fish is kept in water contaminated with harmful chemicals, then also it might take only a few minutes for fish to drown.

Read: How Do Starfish Eat?

Professor Atom

View posts by Professor Atom
Professor Atom is a science enthusiast and alumni of IIT Bombay. According to him, every question can be solved with curiosity and mind mapping. ( Curiosity = Asking Questions = Learning )

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