Popeye Fish Disease: Causes, Treatment & Prevention

An Orange Fish With Bulging Eyes
An Orange Fish With Bulging Eyes
Dr. Mollie Newton
Published by Dr. Mollie Newton PHD| Senior Editor
Last updated: June 11, 2024
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As a fish keeper, you may not have been aware of a disease known as popeye that affects fish, until it reached an irreversible stage. This often deadly condition is commonly overlooked, resulting in many neglected fish. Thankfully, we’ve assembled an extensive guide that details the characteristics and effects of popeye in fish, equipping you to handle such a serious issue.

Article Summary

  • Popeye in fish can be caused by various factors, including physical injuries from tank decor, sharp edges, or other fish.
  • Popeye disease symptoms include one or both eyes bulging outwards, cloudy or smoky eyes, and it is important to not try to pop the fluid as it can lead to complications, and fish cannot regrow their eyes.
  • To treat Popeye disease, consider options such as salt baths, antibiotics, quarantine, and keeping the water clean, while prevention can be achieved by maintaining good water quality, avoiding overcrowding, removing sharp decor, and monitoring your fish for stressors.

What is popeye fish disease?

Popeye disease is an ailment that results in the swelling of the region behind fish’s eyes forcing the eyeball up and out creating a bulging effect.

In more detail the swelling is due to tissue fluid flowing into the space between the eyeball which forces it to “pop.” Any cloudiness or smokiness to the eye is because of damage to the cornea. It can affect any fish species.

What causes popeye in fish?

Popeye fish disease can be caused by a few different problems. One of the easiest ways to determine the cause of popeye disease is whether or not they have a unilateral popeye (only one eye appears swollen) or if both eyes are affected (bilateral popeye).

If there is only one affected eye it is likely that the underlying cause is an injury that has caused severe swelling. Aquarium fish are clumsy creatures and do not have eyelids to protect them from run ins with tank decor, sharp edges or even other fish. Often if physical injury is the cause then you will be able to see evidence of the injury.


If physical injury is the cause of your fish’s popeye you should take into consideration your handling techniques. Using nets with rough edges or sharp-edged tweezers to feed your fish could lead to potential injuries.

If your aquarium fish has two affected eyes the presence of popeye could indicate other potentially dangerous problems such as dropsy, kidney failure, or extremely poor water quality.

Is Popeye bacterial or fungal?

A Fish With Bulging Eyes
(1) A Fish With Bulging Eyes

Popeye fish disease is due to opportunistic bacteria infection. Initially, there is a scratch to the eyeball that results in swelling around the eye, much like how you and I respond to an injury. Eventually, the build up of fluid behind the fish eyes can lead to potential bacterial infections. Fungal infections may occur as a side effect of popeye. They do not cause it.

How Serious Is Popeye Disease?

While popeye disease likely won’t be fatal, exposure to this disease does cause the infected fish to be more likely to catch an infection. Use of Tetracycline, a broad spectrum antibiotic, recommended in moderate to severe cases. Without treatment, popeye can lead to blindness, sudden drastic organ failure, and death.

Is popeye lethal to fish?

Popeye disease isn’t fatal itself and aquarium fish will eventually recover from their ailment. However, infected fish will have a greatly diminished immune system which can lead to a plethora of illnesses including parasitic infections, bacterial infection, fungal problems, and even internal infections.

Symptoms of Popeye Disease

The symptoms of popeye disease are straightforward and relatively easy to identify for most fish. However, fish like the bubble eye goldfish or black moor goldfish already have large protruding eyes which makes popeye hard to distinguish in some fish species.

Symptoms include:

  • One or both eyes bulge outwards
  • Cloudy or smoky eyes

Luckily, the easy identification means that you can begin treating popeye disease quickly, leading to a better chance of recovery.

Like you, your fish will act ill if they have popeye. Uncommon behaviors such as clamped fins, shyness, and no appetite can also be signs of popeye.

How do you know if your fish has Popeye?

If your fish’s eyes are abnormally pushed out of the socket, smoky, or the tissue surrounding the eyeball seems to be poofy and enlarged there is a good chance that they have Popeye disease. Since treatment at the early stages of popeye disease is not invasive it’s better to start to treat conditions if you suspect.


Betta fish are especially prone to diseases such as popeye as many people keep them in fish tanks that are much too small for them. Betta fish require a minimum of 5 gallons, but many people keep them in small, 1 gallon tanks.

Fish Popeye Treatment

The main course of treatment for mild popeye cases is to keep the water clean and monitor any changes for the worse. With improved water conditions popeye has been known to resolve itself, but additional treatment such as salt baths and antibiotics are needed if severity worsens.

Should you Quarantine your fish?

Goldfish at Bottom of the Tank
A Quarantined Goldfish

Yes, the first step to treat popeye disease in fish is to quarantine the infected fish. Placing the affected fish in a quarantine tank makes treatment later easier. If your fish has unilateral popeye disease due to being injured, being placed in an aquarium separate from the main tank will let the fish recover and allow you to monitor the water parameters closely.


A quarantine tank doesn’t have to be elaborate, it can be plastic containers that you perform partial water changes on daily.

If you notice bilateral popeye there could be a more severe infection and placing one fish in a separate tank for quarantine will not protect other fish in your tank. At this point it is better to treat popeye disease for the whole tank.

Check Water Quality

While water quality checks should be performed regularly if you notice popeye disease in fish you should immediately check your ammonia and nitrate levels. As high ammonia levels and poor water quality lead to severe infections fish with popeye disease are at high risk.

If your ammonia and nitrate levels are outside of an acceptable range perform a water change immediately and continue monitoring your fish daily until optimal water conditions are reached.


Other ways to lower ammonia and nitrate levels to an acceptable range is to include biopellets or floss in your tank. These strategies help lower the maintenance needed for messy tanks by increasing your filtering efficiency.

Add Epsom Salt

Epsom salt in a bowl
Epsom Salt In A Bowl

To reduce swelling, you can add epsom salts to your aquarium. Add 1 to 3 teaspoons for every 5 gallons of water in the treatment tank and expect to see results in 3 to 5 days. While doing so, be sure to feed your fish a vitamin rich diet. As epsom salts pull the fluid out of your fish they will also deplete vitamins and minerals in your fish’s body.

Epsom and aquarium salt are not the same thing. Epsom salt can potentially increase the hardness and alter pH levels, whereas aquarium salt is made to not alter water parameters. Additionally aquarium salt heals injuries, decreases the absorption of nitrates, helps with gill function, and assists in invertebrates molting. On the other hand epsom salt is effective to reduce swelling, soothe muscles, acts as a laxative, and is effective against dropsy.


You cannot use aquarium salts in a saltwater fish tank as it is not specially formulated for those conditions. However, you can use epsom salt in a saltwater tank, and many people use it in reef tanks to raise the Magnesium.

Using antibiotics

In cases of severe popeye disease in fish where bacterial infection has set in you’ll need to acquire aquatic veterinary services to receive broad spectrum antibiotic. The antibiotics given for fin rot and other bacterial infections are similar, however for an internal infection the antibacterial medication needs to be administered orally instead of in the water.


If you suspect bad water conditions to be the culprit we recommend treating your community tank with an all purpose antibiotic to help prevent popeye disease in other fish.

How to prevent fish popeye

Preventing popeye disease is the best treatment, and to keep your fish safe you should follow these recommendations.

  1. Reduce overcrowding-one of the leading causes of large amounts of ammonia and nitrates is having an overcrowded tank. Additionally, overcrowding can lead to even peaceful fish fighting amongst themselves potentially causing injury. A larger tank is always better, and having an under-crowded tank is better than an overcrowded one.
  2. Modify decor-if your fish is prone to accidental injuries perhaps you should rethink the decoration in your tank. Abrasive rocks, spiky fake plants, and sharp corners can lead to fish injuries.
  3. Check parameters regularly– poor water conditions can lead to various diseases or health issuses, not just popeye disease. To protect your fish and prevent popeye you should check parameters and all tank equipment for functionality. If your tank or bioload is too large your filter might be underperforming. Maintaining optimal water conditions is essential.
  4. Remove leftover food-uneaten fish food that is left in the tank can lead to elevated ammonia and nitrate levels and lead to detrimental water quality.


Overcrowding doesn’t just refer to the amount of fish in a tank. Messy fish such as cichlids or goldfish can overload your tank and cause a crash to the system.

If one fish is getting popeye disease regularly you might need to look at stressors affecting that fish. Potential issues could include being bullied, improper tank conditions, wrong water temperature, or other underlying problems. Looking out for these issues is the key to prevent popeye.

Should I pop the fluid from the popeye?

No, unlike a pimple popeye in fish is caused by fluid leaking into the area behind the eye. If you attempt to squeeze this fluid out you could rupture the blood vessels in the eye of the fish leading to blindness.

The fluid is the fish’s body’s attempt to heal itself. Much like when you cut yourself and your cells begin to issue a protective covering to help prevent infection and promote healing this fluid is helping the fish heal and should be left alone.

Can fish regrow eyes?

If you’re imagining your fish regrowing their eyes like lizards regrow their tails, then the answer is no. Research has shown that specific fish species- like zebrafish- can regenerate injured portions of their retinas, but this doesn’t apply to every fish. Because it’s unlikely your fish can heal themselves, popeye should always be treated with care. Otherwise, it can result in the loss of the eye or blindness.


In conclusion, popeye can be a serious disease and cause for worry, however it can also be easily identified and treated. Whether your fish is just clumsy, was attacked, or has underlying problems you now have the knowledge on how to treat and prevent future popeye pop ups.

Thank you for reading! If you found the information useful, be sure to take a look at my other guides on this site.

(1) Benson Kua from Toronto, Canada, CC BY-SA 2.0, via Wikimedia Commons

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