Gas Bubble Disease (GBD) in Freshwater Fish

Causes, Treatment, and Prevention

Goldfish bubbles

Tandis / Flickr

Gas bubble disease (also known as GBD) presents as bubbles inside the fish that become trapped within the eyes, fins, or skin. It does not include any swim bladder or buoyancy disorders. This disease starts as a collection of very small bubbles, known as microbubbles, that slowly form larger, more visible bubbles. When left untreated, gas bubble disease may cause tissue to degenerate inside the fish, which can be fatal. There are many ways that microbubbles may be invading your aquarium. Changes in water temperature, atmospheric pressure, or improperly functioning filters can all lead to a buildup of bubbles in the tank. In order to successfully treat gas bubble disease, the origin of the microbubbles must be identified and eliminated.

What Is Gas Bubble Disease?

Gas bubble disease occurs when gasses are supersaturated (dissolved beyond their normal limits) in the water, forming small bubbles that are visible within a fish's eyes, fins, or skin. They may also be present within the internal organs. The gas is most commonly nitrogen, and it can include a collection of small bubbles or coalesce into one or two large bubbles. Carbon dioxide and oxygen bubbles are possible, but these gases are frequently used by fish tissues and readily processed.

What is a Gas Bubble?

When a gas bubble forms inside a fish, it indicates that the fish has gas bubble disease. The bubbles that you see are usually filled with nitrogen.

Symptoms of Gas Bubble Disease in Freshwater Fish

Fish owners can typically see the buildup of bubbles inside the tissue of a fish, but poor water clarity is also a sign that gas bubble disease may affect your aquarium. Many bubbles are visible, but the presence of internal microbubbles must be confirmed by an aquatic veterinarian.


  • Bubbles inside the eyes or underneath the skin and fins
  • External lumps
  • Internal bubbles

Bubbles are visible within the anterior chamber behind the cornea of the eye. Inside the skin, they may present as a visible lump, but sometimes must be felt by moving a hand along the fish. Bubbles can be seen between the fin rays in the clear membrane of the fins. Internal bubbles are not visible and may cause tissue degeneration. It is common to have gas bubbles on both the outside and the inside of fish.

You may also notice that your water clarity has become cloudy. This can be caused by tiny microbubbles held in suspension throughout the tank. The appearance is similar to a glass of water poured too quickly from a faucet. To test your water for bubbles, collect a sample of the cloudy water and allow it to rest undisturbed for 30-45 minutes. If there is sediment in the water, you will notice a film on the bottom of the glass. If it is microbubbles, the water will become clear, and there may be bubbles adhered to the inside of the glass (which resembles a glass of champagne).

Causes of Gas Bubble Disease

There are many causes that can introduce microbubbles into your fish system. While gas bubble disease is typically caused by aquarium equipment that is functioning improperly, external factors that change the water temperature or atmospheric pressure may also lead to a buildup of microbubbles within your tank.

  • Aquarium equipment: The most common cause of gas bubble disease in home aquariums is a barely disjointed pipe or filtration component. Even a pinprick-sized hole allows tiny air bubbles to get sucked in through the movement of the water inside the filtration system. Check your pumps and filter equipment to ensure no air is getting into the pump, which leads to it becoming pressurized and blown into the aquarium. There should not be a high volume of bubbles pumped into the water from your filter.
  • Waterfalls and tank features: Another place where bubbles can be introduced is at the bottom of a tall waterfall or feature. The most common instance occurs when a fish tank is not filled to the top. The impact of the water from the waterfall mixing with the lower water can also introduce bubbles of various sizes. The bubbles may vary depending on your water temperature and bioload.
  • Water temperature: Because the partial pressure of a gas changes with temperature, sudden changes in water temperature can cause bubbles to form. This is most common when water is added to your system that is significantly warmer or cooler than the current water temperature. Unless you are intentionally changing the temperature in your aquarium, it is critical to always test the water temperature before changes. Match the new water to the current temperature. If you need to adjust your tank or pond temperature, go slowly to avoid stressing the fish.
  • Atmospheric pressure: Gas supersaturation in water occurs when the total pressure of gases within the water is higher than the surrounding atmospheric pressure. Depending on how your system is set up and the atmosphere within the room surrounding your aquarium, you may see microbubbles forming during simple atmospheric weather changes. If your fish are experiencing gas bubble disease without a clear cause, try recording the barometric pressure surrounding your tank for a few days and note when the bubbles begin to form or dissipate.

Diagnosing Gas Bubble Disease in Freshwater Fish

Most cases of gas bubble disease can be diagnosed during a physical exam. It is critical to assess all animals within a system that has a potential gas bubble disease episode. An aspirate will be performed to see if the bubble is actually air or clear fluid.

In order to determine whether there are any internal bubbles, an X-ray or radiograph may be taken of your fish. This procedure usually requires sedation in order to get a good picture.

Gas bubbles may also be present within gill tissue. This can be seen on a wet mount of the gills, a common aquatic diagnostic procedure.


The most important treatment of gas bubble disease is to determine the cause of the microbubbles within the system and remove them. It may not be a straightforward process, but preventing additional bubbles from developing within your fish is essential.

Since there are many potential causes, it is critical to eliminate them in order to keep the disease from getting worse. Check the aeration, water pumps, and water flow back into the aquarium, and look for tiny bubbles on plants, décor, or the walls of your tank. Turning off the filter temporarily and checking for new bubbles may help you determine if the filter is causing the gas supersaturation.

It is also important to evaluate all animals within the system to ensure that all those who are symptomatic are effectively treated. De-aeration of the tank `is very important. Your veterinarian will likely remove the bubbles by aspirating them with a very small needle and syringe. Antibiotic therapy is a common addition to any gas bubble disease treatment protocol. Barometric chambers have been employed in some cases if they are available to your aquatic practitioner.

Prognosis for Fish With Gas Bubble Disease

Fish that are diagnosed with gas bubble disease can typically recover and enjoy healthy lives with proper treatment. However, the degeneration of internal tissue caused by this disease can be fatal to fish when left untreated. In severe cases, the buildup of bubbles inside the body may prevent fish from performing regular movements and impact buoyancy, causing them to swim upside down. When treated, internal bubbles will dissolve, allowing the fish to return to their normal state.

How to Prevent Gas Bubble Disease

In order to successfully prevent gas bubble disease, it is important to evaluate all the potential causes and eliminate them from your system. Since plumbing and filtration malfunctions are the most common cause of GBD, start by checking the seals on your aquarium's equipment. Next, maintain suitable water levels by keeping a schedule to add water. Always ensure the temperature remains consistent before introducing fresh water to your tank. This also helps aquarium owners notice leaks early and make any necessary repairs before microbubbles can develop at high levels.

Article Sources
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