Pop-Eye in Fish

What is pop-eye in fish

Pop-eye or exophthalmia is a common condition in which one (unilateral) or both (bilateral) eyes of an aquarium fish become abnormally swollen, looking like they are about to pop out of the socket ^{[1, 2]}. Pop-eye is not a disease itself, but an indication of other underlying disorders ^[1]. However, species like celestial eye goldfish and black moor goldfish have large telescope eyes that are normal and healthy ^[1].

Which fishes are more likely to get pop-eyes

Freshwater tropical fishes

• Betta
• Angelfish
• Koi fish
• Cichlids including oscar, and discus
• Goldfish
• Gourami
• Common molly

Saltwater tropical fishes

• Clownfish

What causes pop-eye in aquarium fish

The actual reasons for eyes popping out in fishes may only be determined by diagnosing the underlying condition. Causative factors may include:

• Exposure to poor water condition is possibly the most common cause of pop-eye in fish ^[2]. Overcrowded aquariums, infrequent water changes, and improper water chemistry (including pH, general hardness, salinity, and the amount of dissolved oxygen) are some of the factors that might affect fishes kept in a water tank ^{[3, 4]}.
• Physical injuries caused by accidentally rubbing the eye against a rough object in the tank, or during a fight with another fish ^[1].
• Parasitic and bacterial infections affecting the sight of an injury ^[1].
• Internal health problems, like a kidney failure, causing body fluids to get accumulated behind the eyeball, putting more pressure on it and gradually forcing it outward ^{[1, 2]}.

Signs and symptoms

Aside from displaying an evident bulge in one or both the eyes, the condition can be identified by the following visible symptoms:

• Cloudy eyes (may indicate poor water parameters) ^[1]
• Bloodstained eyes (often due to some physical injury) ^[1]
• Ruptured eyes (in case of severe pop-eye) ^[1]

How to prevent pop-eye in fish

Aside from maintaining the tank and providing with a nutritious diet, some possible preventive measures for pop-eye include:

Aquarium care

• Perform a partial water change when cleaning the aquarium, removing 10-15 percent of the aquarium volume and replacing it with fresh, chlorine-free water, about every 14-15 days ^{[5, 7]}.
• Clean the walls of your aquarium using filter floss pads every other week, starting from the bottom and then continuing upward ^[5]. Wash any new filter cartridges, carbon packets, or sponges using cool running water before putting them in the aquarium ^[7].
• Check all the vital parameters like pH (ideal range being 6.5 to 7.5), hardness (more than 4.5dH or 80ppm), and nitrate level (below 5ppm in saltwater or 10ppm in fresh water) while changing the tank water ^[5].

Fish care

• Do not use abrasive or coarse fishnets, as they might damage the eyes of your fish ^[2]. Instead of netting the fishes directly, you may use fish nets to drive them into a plastic container ^[2].
• Avoid mixing aggressive species of fishes (betta, oscar, discus, angelfish, gourami, and African cichlids) ^[8] with relatively peaceful ones (killifish, comet goldfish, koi, and firefish) ^[9], because a nervous fish may jump and get knocked into the walls, abrasive rocks, or the roof of the aquarium, which might cause an eye injury ^[2].
• Provide your fish with quality food pellets and flakes to boost its immunity ^[1].
• If there are any injured fish in your aquarium, keep them under close observation so they can be treated promptly at the smallest chance of infection ^[1].

How to treat pop-eye in betta, oscar, angel, goldfish, discus, and other fishes

Your vet will determine the proper treatment depending on the symptoms and underlying cause ^[1]. Commonly recommended treatment measures are as follows:

Treatment at home

Quarantine the sick fish

Shift the sick fish to a quarantine tank to isolate it from the other healthy fishes ^[1]. Keep the quarantine tank clean with regular water changes ^[1]. The infected fish may have to be treated with broad-spectrum antibiotics ^[1]. If a number of fishes have swollen eyes due to infection, then you may need to treat the main aquarium with broad-spectrum antibiotics as per a vet’s advice ^[1].

Soak the affected fish in an Epsom salt bath

Adding about 1-3 teaspoons of Epsom salt per 5 gallons of water in the quarantine tank may help in reducing swelling ^[2]. The application may be repeated as instructed by the vet.

Medical treatment for pop-eye

If the above treatment measures are not successful, inform your vet immediately. Antibiotics like tetracycline, kanamycin or chloramphenicol may be prescribed for treating bacterial infections ^[6].

Can pop-eye be cured

Pop-eye can improve with time if your fish is treated promptly, and is given a good aquatic environment ^[2]. The bulge in its eye may go away within just a few weeks or months, but any damage to the cornea may take longer to heal ^[2].

In case of a minor injury, the pop-eye will resolve once the wound heals ^[1]. However, with delayed treatment or severe damage, the fish’s eye may never heal or in worst cases, it may decay and fall off, causing loss of vision ^{[1, 2]}.

Although a fish is least likely to die from pop-eye itself, underlying problems and complications like septicemia and Hexamita parasitic infections could be fatal ^[2]. A fish affected by both pop-eye and dropsy, caused by bacterial infections, has a lesser chance of recovery, though dropsy itself can be cured with quick and proper treatment ^[1].

The expected recovery rate of pop-eye caused by an organ failure is extremely low ^[1].

Is it contagious for other fishes

Since popped eyes are not a disease but an indication of some infection or other complication, according to aquarium fish-keepers the underlying problems could be contagious, even though pop-eye itself is not.