Why Do Fish Eyes Pop Out When They Die? The Typical Causes

Jennifer Doll

Jennifer Doll


why do fish eyes pop out when they die

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Losing one of your favorite pet fish can be very upsetting, especially if the cause of death isn’t obvious. But sometimes, a fish’s eyes bulge out of its head in death. So, why is that?

The first thing to understand is that not all fish eyes pop out when they die. In fact, that’s a pretty unusual phenomenon that’s linked to a specific disease or situation.

Keep reading to learn why some fish’s eyes pop out when they die.

What Is Barotrauma?

Deepwater-dwelling fish species suffering from a condition called “barotrauma” often die with bulging eyes.

Barotrauma is generally seen in fish landed by anglers fishing in deep water and is caused by rapid changes in barometric pressure. The condition can cause several injuries, including hemorrhaging of the fish’s internal organs, prolapse, torsion, hematomas, loss of vision, and bulging eyes.

Unfortunately, barotrauma usually causes death in fish immediately or very soon after the fish is released. In fact, some fish appear completely unharmed and swim away with no problem, only to die later. That’s why many Fish and Wildlife Service authorities prohibit catch-and-release fishing in lakes beyond a certain depth.


The internal symptoms of barotrauma are not visible to anglers. However, several indicators can be seen clearly by the naked eye, including:

  • Bulging or popping out eyes
  • Gas bubbles under the fish’s skin
  • Bleeding from the gills
  • An expanded swim bladder that causes the fish’s stomach to be pushed right out of its mouth

Generally, it’s game fish such as crappies, large-mouth bass, and walleyes that are affected by barotrauma.

So, why would an aquarium fish die with its eyes popping out?


The most likely cause of fish eyes popping when they die is a condition called “Popeye.”

Popeye can affect any fish species, from goldfish to bettas, and even animals and people can suffer from it!

The correct scientific name for the condition is exophthalmia. The condition is caused by a build-up of pressure behind the fish’s eye, causing swelling and bulging from the creature’s head.

Popeye disease in fish can affect one or both of the eyes, and although the condition is unpleasant, it is much easier to prevent than to cure.

What Causes Popeye?

Popeye has a few causes, making determining the reason for your fish’s condition challenging. Treating the illness successfully is difficult without the correct diagnosis, and getting it wrong can lead to a dead fish.

Unilateral Popeye

Popeye can affect one or both of the fish’s eyes. When only one eye is affected by the condition, it’s referred to as unilateral Popeye.

Unilateral Popeye is usually caused by trauma or injury to the eye, causing a physical injury that can result in fish eye infections. For example, sharp tank ornaments or fights between tank mates are common causes of unilateral Popeye.

Bilateral Popeye

Bilateral Popeye is the term used when both the fish’s eyes are affected; in this case, some kind of infection is typically responsible for the eye swelling.

Parasites, bacteria, or fungi can cause internal infections and are usually part of a range of symptoms, depending on the cause.

Symptoms of Popeye

Spotting Popeye is straightforward since it generally presents several telltale symptoms.

Bulging Eyes

The most obvious symptom of fish Popeye is the creature’s eyes bulging out of its head, which is caused by pressure from behind the eyeball.

Cloudy Eye

In fish with Popeye, the eyes also usually turn milky or cloudy, typically indicating serious damage to the cornea. If the eyes are also bloodshot, trauma is often the cause.

White-Ringed Eyes

Early signs of Popeye are white rings around the fish’s eye or eyes, and you need to start treating the problem immediately.

Other Symptoms

Other common symptoms of Popeye include the following:

  • Not eating
  • Lethargy
  • Hiding from tank mates
  • Resting on the tank bottom for long periods without moving

If your fish demonstrate any of those signs, I recommend checking your water quality and parameters to ensure that ammonia and nitrite levels are zero and nitrates are below 20 ppm.

If a water quality issue is to blame, perform partial water changes and retest the water until the parameters are back at acceptable levels.

Is Popeye Contagious?

Depending on the cause, Popeye isn’t usually contagious. However, to be on the safe side, I recommend quarantining the affected fish and treating it.

Is Popeye Fatal?

Popeye can be fatal if not treated promptly and appropriately, which is why some people think that fish eyes always pop out when they die.

However, if the condition is caused by trauma or injury to one eye, it can usually be treated successfully by using broad-spectrum antibiotics and keeping the aquarium environment clean.

Sometimes, the fish might lose the damaged eye, but it can usually survive adequately without it, especially in a spacious aquarium with a few peaceful community tank mates.

How Can You Prevent Popeye?

why do fish eyes pop out when they die

I believe that prevention is always much better than cure!

So, here are a few simple steps you can take to keep your fish safe from Popeye.

Infection Prevention

You can keep your tank infection-free by keeping it clean and properly maintained. If the water is dirty or contaminated with high ammonia levels, your fish will be stressed, leaving them vulnerable to parasites and diseases.

Keep the tank clean by performing weekly water changes of around 20%, taking care to deep-clean the substrate with an aquarium vacuum to remove organic waste and leftover food.

Maintain the filter system by rinsing the media in old tank water every couple of weeks and replacing old filter media periodically per the manufacturer’s directions.

Overcrowded Tanks

Keeping too many fish in your tank can make it difficult to maintain proper water quality and will overload your filter system.

Overcrowding can also lead to aggression between tank mates, potentially resulting in traumatic eye injuries and Popeye.

Choose Decorations Carefully

Collisions with sharp decorations can also cause eye injuries, so choose what you put in your tank carefully.

I once added a beautiful piece of twisted root to my fish tank, only to see my fancy goldfish catch and tear its trailing tail fin on the decoration. Needless to say, I removed the decoration right away and replaced it with something safer!

Plastic plants are another potentially dangerous tank decoration to avoid. Sharp leaves can easily poke a fish in the eye, causing an injury that could cause Popeye.

Quarantine New Fish

You can keep bacterial infections and parasites out of your main tank by first placing any new fish and invertebrates in a separate tank for a couple of weeks. Once you know the newbies are disease-free, you can introduce them to your main tank.

Aggressive Tank Mates

Aggression between tank mates is a common cause of unilateral Popeye disease. So, if you spot any fish in your tank misbehaving and squabbling, you’ll have to think carefully about whether removing them would be the best course of action.

That situation can be prevented by researching your desired fish species carefully for compatibility before adding them to your main tank and creating a community. Belligerence between individuals usually settles down after a few days. However, if the problem persists, you might need to think about rehoming one of the aggressors for the safety of your other livestock.

Use a Net

Many fish are injured during the process of netting, which can be necessary during tank moves and cleaning.

If you use a net, choose one with a very fine mesh that won’t injure your fish’s eyes or damage his fins, potentially causing a secondary infection that could result in Popeye.

How To Treat Popeye

Of course, the successful treatment of Popeye in aquarium fish depends on the cause of the problem. However, here are two treatment methods that have worked for me in the past that you might like to try.

Physical Trauma

If you think your fish’s Popeye has been caused by physical trauma or injury, I recommend using a salt bath to treat it.

Epsom Salt Treatment

  1. Fill a small bowl with a little water from your aquarium.
  2. Add Epsom salt to the water, following the dosage guide on the packet.
  3. Stir the water to dissolve the Epsom salt fully, and then place the injured fish into the bowl.
  4. Leave your fish in the salt bath for roughly ten minutes.
  5. Float the container in the fish tank throughout the bathtime to maintain the same water temperature.

A salt bath can help to clean a wounded eye and prevent infection while being completely safe for your fish.

Bacterial Infection

The treatment is different if you think that a secondary bacterial infection has caused Popeye in your fish.

Melafix Treatment Method

  1. Start by setting up a quarantine tank and putting the affected fish into it.
  2. When the fish has settled in the quarantine tank, change 50% of the water in the main display tank to remove the cause of the disease and protect your other fish.
  3. Treat the infected fish with aquarium salt and over-the-counter medication, such as Melafix.
  4. Perform a 100% water change in the quarantine tank every few days, remembering to retreat the tank with Melafix and fresh aquarium salt.
  5. After ten days, cease treatment. Your fish should now gradually be recovering and can be returned to your main tank.

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Final Thoughts

Did you enjoy our guide to why fish eyes sometimes pop out when they die? If you did, please go ahead and hit that share button above!

Most fish’s eyes do not pop out when they die. However, some deep-water game fish can experience a typically fatal condition called barotrauma when landed by anglers. Among other symptoms, barotrauma can cause the fish’s eyes to pop out when they die.

However, a disease called Popeye is the most likely cause of a fish’s eyes popping out. Popeye is usually caused by physical trauma to one or both eyes, but a secondary bacterial infection can cause it.

Popeye can usually be cured with prompt treatment, depending on the cause.

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