Just because a fish has bulging eyes doesn't mean there's a problem. Some fish breeds—like the Black Moor goldfish and the Celestial Eye goldfish—are prized for their large telescoping eyes, which are perfectly normal and healthy. Sometimes, however, cloudy and swollen eyes can indicate popeye disease in your aquarium fish.
If you see one or more of your fish exhibiting signs of popeye disease, chances are an underlying infection is behind the scene. This condition can cause your fish to lose its eyes or its eyesight if it goes untreated.
What Is Popeye Disease?
Popeye disease—medically known as exophthalmia—is a condition where the eye of the fish is swollen and protrudes abnormally from its socket due to various underlying diseases. This issue can affect a single eye or both eyes. Eyes may appear cloudy or may even look clear in some cases, other than the obvious swelling.
Signs of Popeye Disease in Aquarium Fish
Fish breeds that normally do not have telescoping eyes can sometimes display a marked swelling of one or both eyes. This swelling is usually caused by fluid leaking into the area behind the eyeball. The eye can be cloudy or discolored if the cornea was ruptured, or it can be bloodstained (in the case of the fish suffering a physical injury). In severe instances, it's possible for infected eyes to rupture without treatment. If this happens, the fish may eventually recover but will be blind in the affected eye.
Causes of Popeye Disease
Multiple causative agents can be responsible for popeye and sometimes the true underlying disorder is never determined. If only one eye is affected (unilateral), it is likely that the condition is caused by an injury rather than a problem with the water chemistry. This is particularly true if only one fish is exhibiting popeye. A swollen eye can be the outcome of a fight with another fish or your fish could have scraped its eye against an abrasive object in the tank. If this happens, look for damage to the eye—a dead giveaway that exophthalmia is the result of an injury. In most injuries, the protruding eye will eventually recede as it heals. However, the fish should be monitored closely, as infection can ensue, causing the fish to lose sight in the affected eye.
Another cause of popeye is an infection. This is most likely seen in both eyes. Infection may be caused by a variety of organisms, including bacteria, fungi, and parasites. If the fish suffers from both popeye and dropsy (edema of the belly), the prognosis is bleak. Internal problems, such as kidney failure or a metabolic issue can result in fluid build-up, making it extremely hard to treat your fish.
Poor water conditions can also contribute to popeye and fish that are sensitive will be affected first. If one or more fish in your tank presents with popeye, test your water to determine if something is amiss with its chemistry. Also consider supersaturation of gas in the water, which can be seen as tiny bubbles on the sides of the aquarium and even in the fish's skin. This can cause gas to accumulate in the eyes and make them swell.
Treatment for popeye will depend upon the underlying cause. If the eye has been injured, perform palliative care using aquarium salt while the eye heals (unless contraindicated). Regular water changes and the monitoring of water chemistry is also recommended throughout recovery time. If water tests indicate a problem—a drifting pH or elevated ammonia or nitrite—correct it promptly to avoid additional stress. And all fish should be fed a high-quality food to support healthy immune systems.
Any fish clearly suffering from a bacterial infection should be moved to a quarantine tank to avoid infecting other fish. Treat this fish with a broad-spectrum antibiotic food recommended by your pet supplier or veterinarian to resolve the infection. If more than one fish is infected, it may be necessary to treat the main tank with antibiotics, as well.
Parasite infestations can be diagnosed by an aquatic veterinarian through skin and gill biopsies and the appropriate treatment can be prescribed to treat the aquarium water.
How to Prevent Popeye Disease
Because popeye is caused by such a wide variety of issues, there is no magic bullet to prevent its occurrence. However, if the tank is well maintained, partial water changes are performed regularly, and the fish are fed nutritional food, the odds of popeye striking is greatly diminished. Monitor the tank water chemistry and observe your fish daily for signs of illness to help tip the scales in your favor. If basic care is followed meticulously, popeye is unlikely to occur. And if it does, it probably won't be fatal.
Aitchtuoh, Fischer. Treating Pop-Eye. Central Florida Aquarium Society