Why Is My Betta Fish Flaring its Gills?

Why is My Betta Fish’s Eye Bulging?

Betta fish have beautiful little eyes, and if you have multiple bettas, you can see that they have individual eye colors! Eyes are extremely important to bettas because they are sight predators. As a result, they will be unable to see their food or and could starve without their eyes. In fact, there are several illnesses that target the eyes, and the most common causes of bulging eyes in bettas.

If you find your betta has one or two bulging eyes, your betta has pop-eye. Pop-eye is a condition in which the skin around the eye becomes inflamed and swollen. As a result, the physical eye to swell and bulge and potentially come out of the socket. If left untreated, your fish will lose its eye and sight.

In this article, we will cover water quality, trauma, eye and abdomen swelling, determining the cause, and treatment.

Water Quality

While it may seem that bettas are prone to pop-eye, the real issue is that bettas are beginner fish. When you start out in any new venture, you will make some mistakes. These mistakes can lead to pop-eye in fish, but they are easy to fix.

When discussing water quality, ammonia, nitrite, nitrate, and temperature are of the upmost concern. In fact, these compounds are leading causes of death in “beginner” fish and cause many other health issues.

Ammonia and nitrite are extremely toxic in any amount, and nitrates need to be 20ppm or lower. For example, ammonia burns fish on the outside, nitrite prevents the blood from carrying oxygen, and nitrate lowers the immune system.

Likewise, keeping fish at improper temperatures will also lower their immune system. If your water has any amount of ammonia and/or nitrite, nitrate over 20ppm, or a temperature that is not between 78-82 degrees Fahrenheit, these can cause pop-eye.

The presence of these harmful compounds will stress your fish, which in turn also affects their immune system. Aquarium water always has bacterial, fungal, and parasitic bodies, but they are normally in low numbers. These low numbers can easily be fought off by your fish’s immune system.

However, if improper water parameters damage your fish’s immune system, it can get pop-eye. Pop-eye is most often caused by opportunistic bacterial infections, but it can also be caused by parasites.

These bacteria take advantage of your fish’s weakened state and infect the eye area. Next, the tissue around the eye responds to the bacteria by raising the temperature and swelling, putting pressure on the eye. This, in turn, leads to the eye protruding, which is pop-eye.


If your fish injures its eye, this is another possible cause of pop-eye. For example, if you have a decoration and your fish runs into it, the tissue around the eye can bruise and swell. The body does this in order to speed repair of the surrounding tissue, but if the injury is severe, the swelling may put too much pressure on the eye.

In this instance, the most important thing you can do is monitor your fish. Secondary infections are very common when it comes to injuries in the water. As previously discussed, the water is full of pathogens, but they only infect fish with weakened immune systems.

When a fish gets an injury, the injury site is open to disease and the immune system is weak while trying to heal the area. For instance, this is the only time you would see a fungus set in, as the fungus can only infect dead flesh.

Secondary bacterial infections are also common, so keep a close eye on the injury site. For example, if the flesh turns extremely red, purple, or gray, you will need to use an antibacterial. Some antibacterial medications will kill the bacteria that keep your tank cycled and free of ammonia and nitrite, so you will need to closely monitor parameters.

If you see fluffy white coming out of the wound, you will need an antifungal medication. After treating the fungus, you will still need to monitor for bacterial infections.

Eye and Abdomen Swelling

If you fish is showing swelling in one or both eyes and the abdomen, you may be seeing early signs of dropsy. To clarify, dropsy is kidney failure in fish, characterized by swelling all over the body. Unlike our kidneys, a fish’s kidney not only cleans the blood, but also regulates the flow of fluid in and out of the body.

Once the kidney is damaged, it is unable to get all of the excess fluid out of the body. As the fluid builds up inside the fish, the fish’s tissues become saturated and swell. Bacteria are the most common cause of Dropsy, so you will need an antibacterial.

As you may imagine, major organ failure in fish does not have a good prognosis. Your best chance is to catch it early, before all the scales “pinecone”, and to treat with Kanaplex and Epsom salt.

You can find Epsom salt at any grocery store or drug store. Even though it is used to treat bloating and digestive issues in humans, unscented Epsom salt can be used to treat similar issues in fish. Add 1 tablespoon per 5 gallons of water to your fish’s main tank.

Kanaplex is a very strong antibacterial that can have negative effects, but it is the only medication known to treat dropsy. You should dose 1 spoon (provided with the medicine) per every 5 gallons of tank water every other day. The treatment is a six-day period, dosing every other day.

During this time, you should do a 50% water change every other day before you dose medication. Be sure to replace any Epsom salt you take out with the water. For example, if your betta is in a 10-gallon tank, you will have to replace 1 tablespoon of Epsom salt with each water change.

Determining the Cause

In order to treat your fish properly, you will have to determine what caused pop-eye. If dropsy causes pop-eye, you will also see swelling in the abdomen. Pineconing will also appear, which is the scales sticking outwards from the body.

On the other hand, if the pop-eye is caused by a bacterial infection, you will likely be able to measure improper water parameters. Test your water with a reliable test kit, such as the API Freshwater Master Test Kit. If you register any ammonia or nitrite, or your nitrates are very high, it is likely that a bacterial infection caused the pop-eye.

If your fish injured itself and trauma caused the condition, you will likely see the injury site. You may also see blood in and around the eye area. The first thing to do in this case is to find out how and where your fish injured itself. Remove any decorations that are potential suspects and check them for sharp areas and small areas your fish may squeeze through.

Another way to determine the cause is to see how many eyes are swollen. If only one eye is swollen, it is most likely injury based. On the other hand, if both eyes are swollen, it is possibly dropsy or a bacterial infection.

The eyes do not have to be swollen to the same degree. From what I have seen, dropsy causes swelling more in one eye than the other, but both eyes are swollen. In addition, the abdomen will be swollen more on one side than the other, but the swelling will parallel the swollen eyes.

Even though dropsy can also be caused by improper parameters and stress, it is much less common than pop-eye. A simple bacterial infection of the eyes is the most common culprit.


Once you have determined the cause of your fish’s pop-eye, you will be able to start treatment. Treatment is essential, as your fish may lose one or both of its eyes without treatment.

In the case of a bacterial infection of the eye(s), most antibacterial medications will work, but Melafix will not. It is a great preventative medication, but it is not strong enough for pop-eye and can injure betta fish if overdosed.

Erythromycin and Kanaplex are the best medications to use and to have on hand. Order one, or both, of these before you need them, as treatment is often time sensitive. Aside from an antibacterial, you should also keep a close eye on your fish to ensure more problems are not cropping up.

In regard to the other causes, treatment for them is the same as discussed above. Unscented Epsom salt and Kanaplex can treat Dropsy and keeping a close eye on an injury is essential. If the injury shows signs of secondary bacterial infections, you should use Kanaplex or Erythromycin.

On the other hand, if you start to see fluffy white fungus, you should use methylene blue. Depending on what is available in your area, these antibacterial and antifungal medications can be replaced with other medications.

In conclusion, pop-eye is the common name for a swollen and protruding eye or eyes. It is most often caused by improper water parameters and resulting bacterial infections. Luckily, you can easily treat it with commonly available medications.

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