Diseases

This disease usually only effects one or two fish in a pond or aquarium, and is rarely markedly infectious. Popeye is some type of infection or fluid buildup that causes the eyes of a fish to bulge out of their sockets. It can be caused by bacteria and infections may range from minor to fatal. Popeye is often an early warning of dropsy. The eyes bulge out abnormally in pop-eye because of an accumulation of fluid either in the eye itself or behind the eye.
Gas Bubble Disease is a result of supersaturation (excess levels) of the water with the gas, nitrogen. Supersaturation occurs whenever the pressure of a gas in the water is higher than the pressure of the same gas in the surrounding atmosphere. When there is this difference between gas pressures, the gas gets pulled too quickly out of the bloodstream, leaving gas bubbles behind. This is what happens to SCUBA divers who ascend too quickly and create a big difference in gas pressures, which leads to the diver getting gas bubble formation or the "bends". In fish, gas bubbles can accumulate behind the eye, making it bulge outward.
Water in a newly filled tank will be supersaturated with gases and you will see the gas bubbles covering the inside of the tank. The more that the water is agitated as you are pouring it in for the first time, the less supersaturation you will have. Agitation of water releases gas from it. Normal aeration will speed up the time that it takes for this excess gas to leave the water. When the bubbles on the tank disappear, then it is safe to put your fish into the new water.
High-powered powerheads, that shoot streams of air into your tank's water, can lead to nitrogen supersaturation. Treatment in this circumstance would be to turn down the powerhead water stream adjustment to it's lowest setting and allow the air pump to be the only source of air. For the next few days, observe your fish. If the pop-eye starts to go away, then it was due to nitrogen supersaturation. If there is no change or the condition worsens, then the pop-eye is most likely due to an infectious cause and probably a bacterial one.
An excess of nitrogen gas can also occur as a result of a large build-up of nitrites and nitrates in the water and has been seen in deep wells and frozen-over ponds and lakes, but probably does not happen to a significant degree in the aquarium. It is always important however to maintain excellent water quality for your fish. Under normal circumstances, there should be no measurable nitrites and the nitrates should be kept at 20 ppm or lower for all but the most sensitive species.
The bacterial causes may manifest themselves as septicemia from such organisms as Aeromonas, Pseudomonas and Edwardsiella, all gram-negative rod bacteria. To diagnose septicemia, you should look for red blotches or red streaks on the body and fins. Bloody splotches at the base of the pectoral fins are often the first indication of septicemia. It is when the bacterial infection attacks the internal organs that the eyes begin to collect fluid. If your fish is still eating, treat by feeding antibiotic food. The most effective medicated food is Medi-Gold, which contains three antibiotics, including kanamycin. Romet B and Tetra medicated food for bacterial infections are alternatives to use, but the Tetra brand food may be less effective due to bacterial resistance that has developed to it's antibiotic, tetracycline. If your fish has stopped eating or seems to be quite sick even with medicated food, then he should be treated with antibiotics in the water. The antibiotics kanamycin (Kanacyn) and minocycline (Maracyn-Two) have gram-negative rod bacterial coverage and can be used to treat septicemia.
Other bacterial causes of pop-eye are from Mycobacteria (fish TB) and Nocardia. Fish infected with these bacteria tend to waste away and may have open ulcers on their bodies. Few studies have been performed to determine which antibiotic is best to treat fish TB. There has been some reported success with minocycline (Maracyn-Two) and kanamycin (Kanacyn). Interestingly, minocycline successfully treats Mycobacterium marinum (fish TB) in humans!
Viral causes of pop-eye have been identified in the fishing industry in channel catfish, trout and salmon. These viral diseases cannot be treated with medication and all fish must be destroyed, as it is very contagious. Even the survivors of these viral diseases are destroyed because they then become carriers of the virus with the potential to spread it to healthy fish.
Pop-eye is very rarely a result of such parasites as Ichthyophonus and flukes. The fungal-like organism, Ichthyophonus hoferi, formerly known as Ichthyosporidium, is not the same as Ich (Ichthyophthirius multifiliis). The disease that it causes is known as Swinging Disease or Tumbling Disease, as fish infected with it rock, sway and even tumble as they swim. No treatment is known and affected fish should be removed from the aquarium and destroyed. Eye flukes (Diplostomum) cause the eye to become cloudy, on occasion to bulge and often leads to blindness. This parasitic infection can only result from a fish being exposed to an intermediate host in it's life cycle and usually that's a snail.
An inadequate diet may result in pop-eye. In this circumstance, you would also expect to see other signs of severe starvation or malnutrition, such as curvature of the spine. It is important to provide a varied diet to meet the nutritional requirements of your fish. Remember that flake and freeze-dried foods provide moderate nutritional adequacy, pellet and frozen foods provide high adequacy and live foods provide the highest.
Pop-eye may be seen with dropsy, which is a condition in which fluid accumulates in the abdomen as a result of dysfunction of the internal organs. A fish's scales will stick out and away from the body, giving it a "pinecone" appearance. Also, the underside or belly may look swollen in dropsy.
A bulging eye may be seen as a result of injury. If both eyes are affected, then trauma is unlikely to be the cause.
Finally, pop-eye can very rarely be the result of a tumor, located behind the eye, pushing it outwards.

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