Fish Pop-Eye

Updated April 21, 2020
Author: Sabi - Fishlore member
Social Media: FishLore on Social Media

Fish Pop-eye is not a disease but is more a symptom of an underlying infection. The fish eye bulges out in this manner because of fluid build up, either behind the eye or in the eye itself. The first signs you will notice is that one or even both eyes are starting to bulge.

Slowly with time it can bulge to such an extent that the fish will look really shocking with the bulge.

Fish Pop-eye


The bulging eye may have a thin layer of 'skin' around it, this is a tough tissue that covers the eye keeping it in the socket and as the eye bulges it stretches the 'skin' with it. The fish may also get less active and show no interest in food. Fungus infections can show up afterwards.

If this disease is not detected soon after it is caught the fish can lose one or both of its eyes and its eye sight. Any impact the eye might be subjected to generally as a result of fighting, can cause this. If its one eye chances are it's injury, if its both then it is possibly a bacterial infection. Bad water quality is a common reason enough to be the cause. High nitrates/nitrites, ammonia, metal or plastic poisoning can be the reason too. Unsuitable salinity can also be the cause.

Bacterial infections, injury and water quality are the most common problems. Vitamin A deficiency, tumors and gas embolism are less common reasons. Pop eye can also be caused by gas bubble disease as a result of oxygen super saturation (excess levels) of the water with the gas, nitrogen.

Super saturation occurs whenever the pressure of a gas in the water is higher than the pressure of the same gas in the surrounding atmosphere, whereby the difference in gas pressures causes the gas to get pulled too quickly out of the fish's bloodstream, leaving behind gas bubbles. The other symptoms of this are the appearance of bubbles under the fish's skin. It's caused by excess oxygen in the water, particularly from filters that blow air directly from outside to inside the tank, and from pressurized tap water that did not get mixed.

Pop-Eye Treatment

The affected fish should be immediately taken out to be separately treated. It is difficult to specify a specific treatment unless the main cause is definitely known. Large daily water changes should help, if not Epsom salts have been used with good results to draw the fluid out. One tablespoon per 5 gallons of water for at least three days. Longer if necessary. Epsom salt isn't really salt (sodium chloride) it is Magnesium Sulfate. If water quality is the problem, a 50 percent water change must be made as soon as possible.

If a new item was added to the aquarium recently, it should be double checked that it is not poisoning the water or letting off chemicals. The quality of the water conditioner that is used should be checked that it has a good opinion by other aquarists.

If the water readings are wrong (high nitrates etc), a 50 percent water change is recommended again and 15-20 percent water changes 3-5 times per week, until the water parameters are correct.

Overstocking is a common problem for high water readings (ammonia, nitrites and nitrates).

Another common reason would be decaying dead fish and fish food. The tank should be thoroughly searched for any dead fish and precautions must be taken NOT TO OVER FEED, and if the tank is overstocked, steps should be taken in finding some of your fish another good home.

If a bacterial infection is the cause we would recommend 'Maracyn', 'Maracyn II', 'eSHa 2000' and an anti-internal bacteria for treatment.

References - Fish Lore Forum members: Carol and Laure Anne
- Wikipedia

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