Swim bladder disorder: why a fish floats or sinks, and what to do

What you are looking at

A fish that cannot hold its position in the water. It bobs at the surface and cannot get down, or lies on the bottom and cannot get up, or swims on its side or nose-down, or tumbles when it tries to turn. It is usually still alert, still interested in food, and visibly frustrated by a body that will not do what it is told. Fancy goldfish are the classic case, bettas a close second, but any fish can do it.

The swim bladder is the gas-filled organ that gives a fish neutral buoyancy, and “swim bladder disorder” is not a disease but a description: something is stopping that organ working, and the something is almost always one of five things. Working out which is the whole job, because the fixes are different and one of them is doing nothing.

1. 1

   Constipation or overfeeding

   Started after a big feed, belly a little round, otherwise well

2. 2

   Gulped air

   Comes and goes, worst right after feeding

3. 3

   Water or temperature

   Any reading above zero, or a cold tank

4. 4

   Infection

   Lethargic, off its food, no better after a week

5. 5

   Injury or body shape

   Sudden after an incident, or lifelong

The five causes, in order of likelihood

1. Constipation and overfeeding. By far the most common. A gut packed with dry flake or pellets that swelled after eating presses on the swim bladder and the fish floats. Fancy goldfish, with their compressed bodies, are built for this problem. The tell: it started after a big feed, the belly is a little round, and the fish is otherwise fine.

2. Gulped air. A fish that feeds greedily at the surface swallows air along with the food, and floats until it passes. Bettas and goldfish again. The tell: it comes and goes, and it is worse right after feeding.

3. Water quality and temperature. Cold water slows digestion to a crawl, and ammonia or nitrite stress makes every organ misbehave. A buoyancy problem in a tank that reads anything but zero, or one that has just had a heater failure, is the water’s problem first.

4. Infection. A bacterial or parasitic infection of the swim bladder itself, or a body-wide infection pressing on it. The tell: the fish is also lethargic, off its food, clamped, or has other symptoms, and the problem has lasted more than a week without improving on the fixes above. Dropsy, a bloated body with scales standing out like a pinecone, is a separate and far more serious condition and needs its own treatment.

5. Injury or deformity. A fall, a fight, a rough net, or in fancy goldfish and balloon-bodied fish, simply the shape they were bred into. The tell: sudden after an incident, or lifelong in a fish that was always a little off.

The fix for the common cases

Start here whatever you think the cause is, because it fixes the first two causes outright and helps the rest.

1. Stop feeding for two to three days. Fish are fine without food for far longer than that, and an empty gut is the cure for constipation and gulped air both. Most cases resolve during the fast.

2. Then feed a cooked, shelled pea. A frozen pea, blanched for a minute, skin removed, mashed for a small fish. Pea fibre moves a blocked gut along, and it is the one home remedy in the hobby that reliably works. One pea, then normal feeding at half rations for a week.

3. Raise the temperature a couple of degrees, to 26 to 28 °C for a tropical fish, slowly. Warmth speeds digestion. Goldfish are cold-water fish, so keep them under 24 °C; for them, the fast is the treatment.

4. Lower the water level if the fish is struggling at the surface, or add a resting place near the top, a broad leaf or a floating plant, so it does not exhaust itself. A fish that cannot reach the surface to gulp air in a deep tank, a betta especially, can drown.

5. Feed differently afterwards. Soak dry food for a minute before it goes in so it swells in the bowl and not the fish, or switch to sinking pellets and frozen food. Feed less, and feed once a day.

In the app — a checkup with a photo of the fish and your latest readings sorts the digestive case from the infection: Finley checks the symptoms against your water and gives a plan sized to what he sees. The follow-up check-in a few days later asks whether the fish is swimming level yet, and the journal keeps the date it started, which is the fact that decides whether this is a fast or a medication.

Run a checkup on the fish →

When it is the water

Before any of the above, test. Ammonia or nitrite above zero means a water change today and the ammonia emergency plan; a buoyancy problem is just one of the ways a poisoned fish shows it. A temperature below 22 °C in a tropical tank means the heater, not the fish. And a tank with nitrate above 40 ppm has a fish with no immune margin, which is how the infection cases start; the water-change guide is the long answer.

When it is an infection

If a week of fasting, peas and warmth has changed nothing, and especially if the fish is lethargic, clamped, off its food, or losing colour, treat it as a bacterial infection. Move it to a hospital tank if you have one, keep the water immaculate with daily 30 % changes, and use a broad-spectrum aquarium antibacterial dosed for the tank’s actual volume, for the full course on the label. Some fish recover fully; some are left with a permanent tilt and live years with it, eating and greeting you as before. A fish that stops eating and stops responding is the point at which the kind thing is to let it go, and there is no shame in a decision made for the fish.

Common questions

Can a fish recover from swim bladder disorder?

Usually, when the cause is food or air, and within days: the fast and the pea fix most cases outright. Water-quality cases recover as soon as the water does. Infections are slower and less certain, and a fish that recovers from one may keep a slight tilt for life without it bothering them. Deformities and old injuries do not recover, but a fish that eats and moves about is not suffering, and many live for years like that.

Do peas really cure swim bladder problems?

For the common cause, yes. A cooked, shelled pea is fibre that moves a blocked gut, and a blocked gut pressing on the swim bladder is the usual reason a fish floats. It does nothing for an infection or an injury, which is why the pea comes after a two-day fast and before any medication: if the pea fixes it, you have your answer.

Is swim bladder disorder contagious?

No. It is a symptom, not an infection, and even when the cause is bacterial the bacteria involved live in every tank and only trouble a fish whose defences are down. Two fish with buoyancy problems in one tank are two fish in the same water, so test it.

Should I euthanise a fish with swim bladder disorder?

Not while it is eating and interested in life, however odd it swims. Fish with a permanent tilt manage well with a lowered water level and food that comes to them. The time to consider it is when a fish has stopped eating, stopped responding, and is being pushed about by the current with no ability to right itself, and the fixes above have had their two weeks. Clove oil is the humane method; ask a vet or a fish shop for the dose.