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Some day you may find, as you are staring into your favorite fish’s adorable eyes, that *gulp* one of his eyes is HUGE! Your fish is most likely suffering from pop-eye, which is also known by the medical term, exophthalmus. Humans with an over active thyroid can have exophthalmus and if you remember Marty Feldman from the movie “Young Frankenstein”… he had pop-eye! Some fish, such as the Black Moor, normally have eyes that are bulging or “telescoping” and this is not considered to be pop-eye. Pop-eye is not a disease itself, but rather it is a sign of some underlying problem.
The signs of pop-eye are that one or both eyes start to bulge out. Over the next week, the eye may bulge out even more and sometimes to the point that your once adorable fish is really quite grotesque to look at (the infamous Quasimodo stage!). You may see a large ring of white “skin” around the base of the eye. This tough tissue, that helps to hold the eye in its’ socket, is being stretched as the eye bulges. Your fish may show other symptoms such as being less active and not eating well.
The eyes bulge out abnormally in pop-eye because of an accumulation of fluid either in the eye itself or behind the eye. The many causes of pop-eye include infections from bacteria, viruses and parasites, as well as from water nitrogen supersaturation (gas bubble disease), water quality problems, tumors, internal (metabolic) disorders and nutritional deficiencies. Treatment of pop-eye is based on identifying and treating the underlying problem.
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 its’ 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 25 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 its’ antibiotic, oxytetracycline. 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 minocycline (Maracyn-Two) and kanamycin (K-mycin), have gram-negative rod bacterial coverage and therefore kill the bacteria which cause 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. Minocycline successfully treats Mycobacterium marinum (fish TB) in humans, so it makes sense that this antibiotic should work for the same infection in fish.
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 the Swinging Disease or the Tumbling Disease, as fish infected with it rock and sway 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 its’ 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, 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. The most aggressive treatment for this very often fatal condition includes treating your fish for the first three days with a medication, such as Rid-Ich+, for external parasites in a hospital tank. This is then followed by rapidly raising the water temperature to 86*F, keeping the oxygen levels high and treating for a bacterial infection as outlined above for septicemia, for as long as 2-4 weeks. Epsom salts are to be used at the rate of 1/8 of a teaspoon per five gallons of water. Do not use aquarium or other similar salts.
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.
The good news is that pop-eye is not often fatal, especially if given proper treatment. Pop-eye will sometimes even go away on its’ own with no treatment. As pop-eye is generally not very contagious, one fish expert, Dr. Chris Andrews, recommends observing your fish with pop-eye, while left in the main tank, to see if he gets better on his own or not. If the other previously healthy fish in the tank begin to get pop-eye, he then recommends isolation and treatment of the affected fish. I personally would advise that you search carefully for the cause of the pop-eye as discussed in this article and treat accordingly. If you cannot figure out the cause, then I recommend treatment with either Maracyn-Two or kanamycin, for a possible bacterial infection, in a separate hospital tank. While the main tank may be treated with these antibiotics without harming its’ biological filtration, treating in a hospital tank allows you to isolate the sick fish from the others and medicating a smaller tank means lower medication costs.
Even with proper treatment, your fish may be left with a grotesque eye and fish have even been known to “lose” the eye, that is, the eye becomes detached from its’ socket. Losing an eye is not necessarily traumatic for a fish. Fish can live a relatively normal life with just one eye, except that they can have problems with depth perception, that is, knowing how close or how far things are away from them. This can make swimming and eating a bit of a challenge. A fish that is blinded in one eye should not be destroyed, as they most often can live out a healthy and full life!
The Complete Aquarium Problem Solver by Kevin W. Boyd, Tetra Press, 1993.
The Complete Idiot’s Guide to Freshwater Aquariums by Mike Wickham, Alpha Books, 1998.
Fish Disease: Diagnosis and Treatment by Edward J. Noga, D.V.M., Iowa State University Press, 2000.
Handbook of Fish Diseases by Dieter Untergasser, T.F.H. Publications, Inc., 1989.
The Manual of Fish Health by Chris Andrews, Ph.D., Tetra Press, 1988.