Popeye in fish: bulging eye causes, treatment and recovery
One bulging eye is usually an injury; both means the water or an infection. How to tell which, the Epsom salt fix, and how long the eye takes to heal.
By Xavier Jodoin
In short
Popeye is fluid or gas pushing the eye out of its socket. One eye means an injury or a local infection; both eyes mean the water or a body-wide infection. Test and fix the water, move the fish to a hospital tank with Epsom salt at one tablespoon per 40 litres, and add an antibiotic only if it is also lethargic or the eye is cloudy and getting worse. A mild case recedes in one to three weeks; a bad one may cost the eye, but the fish usually lives.
What you are looking at
An eye that stands out from the head further than it should, sometimes so far that it looks about to fall out, sometimes with a cloudy film over it or a ring of blood behind it. The fish may be otherwise normal, or it may be listless and off its food. Fish cannot blink or close their eyes, so a swollen one is very obvious and very alarming — and, in most cases, less serious than it looks.
Popeye — exophthalmia, if you want the word — is not a disease. It is fluid or gas building up behind the eye and pushing it forward, and the useful question is not “what is it?” but “what is behind it?”. The answer is almost always one of four things, and the first thing to notice is whether it is one eye or both.
One eye points to something local: an injury — a scrape on the decor, a rough net, a fight with a tankmate, a bump during a water change — or a localised infection that got in through one. Fish with big eyes (telescope goldfish, some cichlids) and fish in tanks with sharp rock or crowded tankmates get this most.
Both eyes points to something systemic: water that has been bad for a while, a bacterial infection in the body that has reached the tissue behind the eyes, or, less often, gas supersaturation — microbubbles in the water from a leaking pump seal or a cold tap-water change into a warm tank, which you will also see as tiny bubbles on the glass and the fish’s fins. Both eyes bulging together with a swollen body and raised scales is dropsy, which is its own, far more serious problem.
The fix, in order
1. Test the water. Ammonia, nitrite, nitrate, pH and temperature, today. Popeye in both eyes in a tank that has been reading nitrate in the 40s, or that had an ammonia spike last week, is the water’s problem first, and clean water cures it more often than any medication. Anything above zero for the toxins or over 40 ppm nitrate means a 30–50 % water change now and daily testing until it clears; then a proper weekly schedule.
2. Move the fish to a hospital tank. A bare 10–20 litre quarantine tank with a heater, an air stone and a sponge filter, and nothing it can scrape the eye on. In a community, an injured eye gets picked at, and the medication below is far cheaper in 15 litres than in 150.
3. Epsom salt. Magnesium sulphate at one tablespoon per 40 litres (10 gallons), dissolved first. It draws fluid out of the tissue behind the eye and reduces the swelling, and it is safe for every fish. Keep it up with daily 25 % water changes, re-dosing for the volume replaced, for a week to ten days.
4. An antibiotic, only if there is a reason. A single bulging eye on a fish that is eating and active is an injury, and an antibiotic will not help it heal faster. Add one when the eye is cloudy and getting worse, when there is blood or pus behind it, when the fish is also lethargic and off its food, or when both eyes are involved and the water tests clean — those are infection. A broad-spectrum antibacterial (kanamycin or a nitrofurazone product) dosed for the hospital tank’s volume, carbon removed, the full course on the label.
In the app — a checkup with a photo of the eye from the side and from above, plus your readings, tells you whether this is an injury, the water or an infection, and gives a plan sized to it; Add plan to my schedule books the salt and the water changes as daily tasks.
How long it takes, and what to expect
A mild case recedes over one to three weeks, usually faster than it appeared. A bad one — an eye that has been bulging for weeks, or one with a rupture — may leave the eye clouded, shrunken or lost. That sounds worse than it is: a one-eyed fish feeds, swims and lives a normal life, and keepers routinely keep them for years. What it must not do is go back into a tank with the tankmate or the decor that did the damage.
The eye that does not recover is the eye where the cause was not found. Clean water, and a week of watching who chases whom at feeding time, finds it in most tanks.
Common questions
Is popeye contagious?
No. The swelling itself cannot pass to another fish. If the cause is a bacterial infection, the bacteria are already in the water and only affect a fish whose defences are down; if the cause is the water, every fish is in it. Treat the tank’s chemistry for everyone and the eye for the one fish.
Will the eye go back to normal?
Usually, if the cause is fixed. A mild case recedes in one to three weeks with clean water and Epsom salt. An eye that has bulged for weeks, or that has ruptured, may stay cloudy, shrink or be lost — and a one-eyed fish lives a normal life. What decides it is how quickly the water or the injury behind it was dealt with.
Does Epsom salt help popeye?
Yes, and it is the first thing to reach for. Magnesium sulphate at one tablespoon per 40 litres draws fluid out of the swollen tissue behind the eye and is safe for every fish. It does not treat an infection, so a fish that is also lethargic, or whose eye is cloudy and getting worse, needs an antibiotic as well.
One eye or both — does it matter?
It is the most useful thing you can notice. One eye is nearly always local: an injury on the decor, a rough net, a fight, or a small infection that got in through a scratch. Both eyes is systemic: water that has been poor for weeks, an infection in the body, or gas supersaturation from a pump leak or a cold water change. One eye needs a hospital tank and salt; both eyes needs the water tested first.