Why Is My Fish Swimming At The Top Of The Tank? [Explanation]

Aquariums beautify spaces in our homes, improve our sleep quality, reduce stress levels, lower blood pressure, and bring a calming effect to kids.

However, proper care and maintenance are needed to keep the fish alive.

Why are my fish swimming at the top of the tank

In most scenarios, aquarium fish swim and hang out at different depths of the aquarium.

Therefore, if you find your fish swimming at the top of the tank, then you should be concerned.

One of the main reasons is low oxygen levels.

Here are some of the things that can cause your fish to swim at the top of the aquarium tank:

Fish Is Swimming At The Top Of The Tank Due To A Lack Of Oxygen

Your fish may swim at the top of the tank mainly because of a lack of oxygen.

Fish breathe dissolved oxygen.

Therefore, if the oxygen level is lower at the bottom of the tank, they will swim to the top, where dissolved oxygen is always higher.

Thanks to the interaction between air and water that occurs at the surface.

The aquarium’s dissolved oxygen level is lower when you see your fish gasping for air and swimming at the top of the tank.

Before you conclude that the issue is due to lack of oxygen, you should note if it’s one fish or all the fish in the aquarium.

If it’s one fish, it may be injured or has problems with the gills.

But if all the fish in the aquarium gasps for air, the oxygen level is low.

You can rectify this problem by changing one-third of the water in the aquarium.

Fish Is Swimming At The Top Of The Tank Due To Diseases

Aside from low dissolved oxygen levels, your fish may swim at the top of the tank because of a disease.

One common disease affecting how the fish swims in the tank is the swim bladder.

This disease affects the fish’s equilibrium.

It can make the fish swim at the bottom or top of the tank.

Additionally, it can make the fish swim sideways or upside down.

Some of the major causes of the swim bladder are constipation and overfeeding.

You may notice that this condition typically appears after feeding your fish and disappears afterward.

To avoid such a disease, you should avoid overfeeding your fish.

Furthermore, you should feed it more fish, oranges, green peas, or even melon to prevent constipation.

See also: How To Treat Swim Bladder Disease In Fish

They Swim At The Top Because Of Ammonia & Nitrate

Another issue that can make your fish swim at the top of the tank is excess ammonia or nitrate, or both, in the aquarium.

If the level of ammonia or nitrate is excess, it will be hard for the fish to breathe.

That’s why they may be forced to gasp for air at the top of the aquarium.

For this reason, you should always ensure that the PH level in the aquarium is at the recommended level.

If your aquarium has high levels of ammonia, it makes the fish produce extra mucus.

As a result, it reduces the effectiveness of the gills, as it hampers them from inhaling oxygen as usual.

On the contrary, excess nitrate in the aquarium leads to changes in hemoglobin, which carries oxygen in the blood.

As a result, the fish gasps for oxygen even more.

Some Types Of Fish Swim At The Top Of The Tank

Surprisingly, not every fish you see swimming at the top of the aquarium tank is gasping for oxygen.

Some types of fish love swimming at the top of the tank.

So, before you conclude that it lacks oxygen, you should learn more about the kind of fish you have in the aquarium.

The fish that love swimming at the top of the tank are hatchet fish, zebrafish, and guppies. These fish naturally swim at the surface in the wild to access food first.

However, if any of these surface fish stay in one place for a long time and show signs of gasping, it should indicate low oxygen levels in the water.

They Remember It Is Feeding Time

At times, fish swimming at the top of the tank doesn’t mean there’s a problem.

Some fish types have sharp minds and can learn and remember the time that you always feed them.

My fish is swimming at the top of the tank why?

Hence, they may link your presence in the room with feeding them.

This is common if you usually feed them at a specific time.

Fish Is Swimming At The Top Of The Tank Because Of The Temperature

Temperature and heating are other possible causes of your fish swimming at the top of the aquarium.

Note that warm water holds less oxygen.

Therefore, you should always keep an eye on your aquarium and ensure the water temperature is fine.

It should not heat up, affecting the aquarium’s oxygen level.

You may be forced to change the water frequently in the summer.

Fish Is Swimming At The Top Of The Tank Due To Heat

Besides, the aquarium heater may also malfunction.

If this happens, the water may overheat and cause oxygen levels to drop drastically.

In such a case, you should replace the heater immediately, as increased temperatures can kill your fish.

Fish Is Swimming At The Top Of The Tank Because Of Overcrowding

Excess fish in the aquarium can also cause dissolved oxygen levels to drop in the tank.

The overstocked fish will compete for the same air while polluting the water.

Within a short period, you will see your fish swimming at the top of the tank and gasping for air.

To avoid such a problem, you should inspect the capacity of your aquarium and stick to the “one gallon per inch of adult fish” rule.

This will enlighten you if you have added more fish than the aquarium can handle.

Aside from that, you will have to consider that some fish are very aggressive, while others are larger.

How To Keep Water Tank Fish Friendly

Ensure that you purify the water you use in the water tank.

Doing so ensures the safety of your pet fish.

Therefore, you must avoid using tap water because although it is okay for human consumption, it contains disinfectants like chlorine that are harmful to your pet fish.

You can also replicate seawater by adding salt and other nutrients to your water tank.

To spruce things up, you can make your fish happy by giving it a full ecosystem by adding real and living plants into the water tank.

You can also add some rocks, corals, or even a shipwreck hideout.


If you notice that the fish in your aquarium is swimming at the top of the tank, you should take quick action to know their situation.

Low oxygen levels, diseases, excess ammonia, dissolved gases, or even excess nitrate can suffocate and kill your fish.

As a result, you should find a solution as quickly as possible to avoid suffocating your beloved fish.

Besides, you should also maintain good aquarium practices, such as checking the water temperature and PH levels.

Also, you should regularly aerate the water by changing one-third of the water more frequently.

We hope you have found the answers you’ve been looking for!