Why Is My Fish Coming To The Surface? (Complete Information)

As an aquarist, you may sometimes discover some strange behavior of your fish, like coming or staying at the tank’s surface, that might raise several questions in your mind. So, why is my fish coming to the surface? Is it normal? Let us find out.

Lack of oxygen is the root cause behind your fish coming to the surface. However, other factors like poor water conditions and overcrowded tanks can also make your fish come to the surface. Consider maintaining good water conditions and adding an air pump to the tank to ensure enough oxygen.

In the below article, we will discuss all the reasons behind your fish coming to the surface.

Why does fish swim at the surface of the tank?

If your fish is coming, staying, or swimming at the tank’s surface, lack of oxygen is the reason.

When oxygen is deficient in the water, fishes come to the surface to gasp air from their mouth.

Most oxygen is present at the surface, where air and water interactions occur.

Affected gills will also make your fish trouble breathing, and they will come to the surface to gulp air.

Is it normal for a fish to keep coming at the surface?

It depends on the fish species, as some fish have such swimming behavior.

Fish like corydoras have a habit of coming to the surface and gulping air from their mouth.

Also, fishes like gourami and betta fish breathe air from the surface of the water, which is entirely normal for them.

However, the fish coming at or staying at the surface are not supposed to indicate inadequate water conditions.

Lack of oxygen in the water is the primary reason for such behavior of a fish.

What are the reasons behind oxygen deficiency in the tank?

All these are the possible reasons for your fish swimming at the surface of the tank:

  1. Lack of aeration in the water
  2. Poor water conditions
  3. Overcrowded tank
  4. Inadequate water temperature

Lack of aeration in the water

Lack of aeration in the water is the primary reason behind oxygen deficiency in the fish tank.

There should be a movement in the water to oxygenate the fish tank.

At the tank’s surface, the exchange of two gases takes place. 

Oxygen goes from the air into water, and carbon dioxide goes from water into the air.

When the surface is disturbed with movement, the rate of exchange of gases increases, which means more oxygen will dissolve in the water.

So, if there is no movement/ aeration in the water, there will be a lack of oxygen in the water.

Poor water conditions

A tank with poor water conditions will lack oxygen.

Excess decomposition of organic matter and elevated pH level in the tank results in ammonia poisoning, affecting your fish’s gills and making it harder for them to breathe.

Inadequate water temperature can result in a lack of oxygen level in the water.

Excessive waste in the water increases ammonia and phosphate levels, lowering oxygen levels.

Overcrowded tank

An overcrowded tank will make your fish come or stay at the tank’s surface.

A crowded tank lacks space and oxygen both in the tank, making your fish come to the surface.

An overcrowded tank comes with all these issues:

  1. Your fish will not get enough space to live and swim comfortably.
  2. Your fish tank will get dirty faster than usual.
  3. An overcrowded tank will be oxygen deficient as all fish rely on the same oxygen source.
  4. There will be excessive waste which will increase the risk of ammonia poisoning in your fish.

Inadequate water temperature

Inadequate water temperature will also result in an oxygen deficit in your fish tank.

A hot water temperature will hold less oxygen than a cold water temperature.

Your fish will become hyperactive in hot water temperatures and show erratic swimming patterns to release excessive energy. 

Or they will sit at the bottom of the tank as in warm water; most of the oxygen is present at the bottom. 

How to fix such issues?

Ensure all these things to fix and prevent such issues in your fish tank:

  1. Ensure proper aeration in the tank.
  2. Avoid overcrowding your fish tank.
  3. Maintain good water conditions.
  4. Ensure adequate and stable water temperature.
  5. Keep your fish in a big size tank.
  6. Add live aquatic plants.


We must ensure proper water movement in our fish tank for enough oxygen.

A good filtration system will help keep the tank clean and create enough movement at the surface to exchange gases.

You can turn the pipe of the filter (from where the water is coming into the tank) towards the tank’s surface as it will help you to disturb the surface and create movement.

Adding an air pump is also good for aeration in the tank.

The bubbler will release bubbles from the bottom of the tank, which will reach the surface and burst, creating a movement at the surface.

Avoid overcrowding

An overcrowded tank will lack oxygen as there will be only one source of oxygen for all the fish, and there will be a lack of oxygen in the tank.

Also, more fish means more waste, resulting in poor water conditions.

A tank with poor water conditions will lack oxygen.

To ensure you are not overcrowding your fish tank, follow the one-inch one-gallon rule, which means one inch of fish per gallon of water.

Good water conditions

Perform a weekly water change of 35% to keep your water clean.

Add a good filtration system with biofilter media to keep the water clean and protected from harmful toxins like ammonia and nitrite.

Also, get rid of excessive debris in the substrate by siphoning them out using a gravel siphon.

Keeping your tank water clean and free of harmful toxins will help you keep the water well-oxygenated and safe for your fish.

Adequate and stable water temperature

Ensuring adequate and stable water temperature is necessary to avoid oxygen depletion issues.

Every freshwater fish have their own adequate water temperature in which they thrive.

So, ensure to provide your fish with adequate water temperature.

To ensure stable water temperature, add a heater to your fish tank. 

Big size tank

Keeping your fish in a big size tank will also help you ensure enough oxygen in the tank.

The simple logic behind this is more the big will be the tank, the more will be the surface area.

A larger surface area will exchange more oxygen and release more carbon dioxide.

Add live aquatic plants.

Adding live aquatic plants will help you keep the water well-oxygenated and clean.

However, ensure that you don’t add excess live plants as plants release oxygen and consume carbon dioxide in the daytime, but at night it is vice versa.

Also, provide proper lighting to your live plants, as poor lighting will result in plants consuming oxygen instead of carbon dioxide.


  1. Lack of oxygen is the root cause behind your fish coming, staying, or swimming at the tank’s surface.
  2. However, other factors like overcrowded tanks, poor water conditions, and inadequate water parameters can make your fish come to the tank’s surface.
  3. You can fix such issues by ensuring proper aeration, maintaining good water conditions, and adding live aquatic plants to your fish tank.
  4. Maintaining ideal water parameters and providing ample tank space helps fix such issues.

Reference: ResearchGate

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