Why is my goldfish gasping for air? Lack of oxygen | Hungry | Why?

Have you ever noticed your goldfish at the top of their aquarium (Hopefully Not A Bowl) gasping for air?

Often this can get overlooked because people think they’re just searching for food. Whilst this can often be the case, but not all the time, it could be a sign that all is not well in your aquarium.

There are many tell-tail signs in fish keeping that the water quality is not correct and if left, could harm your fish and even cause them to die.

Why is my goldfish gasping for air? Lack of oxygen in an aquarium is one of the most common issues with goldfish and tropical pet fish. Signs of low oxygen are gasping, lack of hunger, inactive fish and strange swimming behaviors. Consider adding an air pump, increase surface area and increase water movement which will increase oxygen in the water.

There are four main reasons why your goldfish is at the top of your aquarium sucking in air:

  • Lack Of Oxygen
  • Searching for food
  • Diseases
  • Temperature

Let’s take a look at each possible reason that could be causing your fish to gasp for air in more detail.

Lack of Oxygen

Did you know that you can also have too much oxygen in your aquarium? Yes, too much oxygen can lead to lethal gas bubble disease. This is where the fish breathes in over-oxygenated water and it leaches out of their bloodstream creating bubbles in their body tissue. This then appears in the shape of bubbles on the gills, eyes, and fins of your fish. Invisibly, it can also build up in the fish’s heart and lead to death.

Water naturally holds oxygen but this is a limited resource. Once it has been depleted your fish will start to suffer. Fish obtain their oxygen from the surface of the water where a process is known as a ‘gas exchange’ takes place. It is known as an exchange because the air and water do a trade swapping CO2 (carbon dioxide) from the water and O2 (oxygen) from the air. This is a useful and continuous trade since fish breathe in oxygen and give off carbon dioxide.

Read one of our article on Oxygen and how it can affect your fish.

Searching for food

I’m sure you have seen your fish at the top of the aquarium gulping in large amounts of water. This isn’t always a bad thing. Fish will often go in search of food at the top surface of the water; just like the image at the top of this article.

a good supply of oxygen is needed in an aquarium
A good Supply Of Oxygen Is Needed In All Aquariums

Fish are natural scavengers and will always be in search of food – even when they are full and don’t really need more food.

Their natural instinct is to go to the top of the aquarium and gulp water through their gills and find food. This can often look like they’re gasping for air when in fact it’s a natural process and is nothing to worry about.


Many diseases in fish attack the gills and the gill tissues.This can damage the tissues or causes the fish to produce extra mucus that could reduce the amount of oxygen they can extract.

Look out for rapid breathing, spots, lack of appetite, fungus growth and clamped fins – all signs that your fish may have a disease. If this is the case urgent and fast treatment will be needed or the issue could spread through the whole aquarium rapidly. Read our guide on Tropical Fish Disease for more help and information.

Treatment for gill disease in ColdWater and Tropical fish is an anti-bacterial medication which is added to the water. You will need to remove any carbon filter material whilst treatment is in process but remember to return it once all signs of disease has gone away.

We use API Pimafix Pond and ColdWater anti-bacterial treatment for our Goldfish and Koi from chewy.com


Controlling the temperature of your aquarium to the specific requirements of your species of fish it paramount. The warmer your aquarium water gets, the less oxygen it is able to hold. By monitoring the temperature constantly, you will ensure the optimum water temperature for your fish. In general the average tropical fish tank should be about 24-28°C/75-82°F and ColdWater tanks should not exceed 23°C/73°F.

In hot weather temperature can rise suddenly which will deplete oxygen supplies. You will need to do two things. Firstly, try to reduce the temperature of the aquarium or at least stabilize it so there are no sudden rises. We use plastic pop bottles filled with cold water and floated in the top of the aquarium. This will help in extreme hot weather. Secondly, increase the air supply into the aquarium. Add another air pump or increase the surface water movement. Read our review on the 9 Quietest Air Pumps available online.

Conclusion: Why is my goldfish gasping for air?

Although we have focused on goldfish in this article, the basic principle can apply to all fish. Gasping for air at the top of an aquarium is never a good sign for any type of fish, tropical, cold water or saltwater. Immediate action is required and you shouldn’t take it lightly.

Reacting quickly to a lack of oxygen in your aquarium could save your fish.