Swim bladder disease in fish: signs, causes and what to do

"Swim bladder disease" is a symptom, not one disease: it means a fish can't control whether it floats or sinks. The best first steps are to test your water, stop feeding for two to three days, and then feed smaller meals of sinking food.

Many cases in fancy goldfish and bettas are caused by eating too much, too fast. Those usually improve within days. If the fish also looks bloated, has raised scales or bulging eyes, or doesn't improve after a week, something more serious is going on.

How to identify it

The swim bladder is a gas-filled sac inside the fish that works like a life jacket. When something presses on it, inflates it, or damages it, the fish loses its balance. You may see:

Floating: stuck at the surface, often tilted or upside down, struggling to swim down. Part of the body may stick out of the water.
Sinking: lying on the bottom, and only reaching the surface with great effort.
Swimming head-down, tail-down or on its side.
A swollen belly, often more on one side.
The fish still eats and looks alert. This is a good sign: feeding problems are more likely than serious disease.

Who gets it most: fancy goldfish (orandas, ryukins, pearlscales and other round-bodied types) and bettas. The short, round body of fancy goldfish squashes their organs together, so anything in the gut can push on the swim bladder.

When it's a problem

Normal: fancy goldfish are clumsy swimmers. A brief wobble or tumble is fine if the fish rights itself and carries on. Some fish rest on the bottom or at the surface by nature (many catfish, plecos and hatchetfish, for example).
Early: a slight tilt after meals that goes away within a few hours. Usually caused by feeding.
Serious: the fish can't right itself for a day or more, or the problem keeps coming back.
Emergency: a floating fish with skin drying out above the water, or a fish that is also bloated with scales sticking out (see dropsy), has bulging eyes, red streaks, or is gasping. Act today.

What to do right now

Test the water for ammonia, nitrite and nitrate. If ammonia or nitrite is above zero, change 30 to 50% of the water with dechlorinated water at the same temperature. See the ammonia guide.
Stop feeding for two to three days. Healthy adult fish can safely go this long without food, and it lets the gut empty.
Check the temperature. A sudden drop slows digestion. Keep goldfish around 20 to 24°C (68 to 75°F) and bettas around 25 to 28°C (77 to 82°F).
Help a floating fish. Lower the water level a little, dim the lights, and add floating plants or a leaf the fish can rest under. Keep exposed skin wet.
Help a sinking fish. Keep the bottom clean and smooth so the fish doesn't get sores. Lower the water level so it has less far to go to breathe.
Move it away from bullies if tankmates are picking on it. A breeder box works well.

What to do next

Days 3 to 7: change how you feed. When you start feeding again, offer very small meals once or twice a day.

Feed sinking food, or soak dry food in tank water for a few minutes first. Fish gulp air when they snap at floating food at the surface, and dry flakes and pellets swell in the gut. One aquatic vet notes that surface feeding often causes temporary floating in hungry goldfish, and switching to sinking food fixes it.
Add variety: thawed frozen daphnia or brine shrimp suit both goldfish and bettas.
Don't overfeed. See the overfeeding guide.

About peas. Feeding a cooked, skinned, mashed pea is an old remedy, and some vets and goldfish experts still suggest it after a short fast. Others argue that true constipation is rare in freshwater fish and that peas don't fix the real cause. Peas are plant food: an occasional bit won't hurt a goldfish, but bettas are meat-eaters and don't digest them well. The parts everyone agrees on are the fast, smaller meals and sinking or soaked food.

Week 1 to 2: if it isn't improving. If the fish still can't balance after a week of good water and careful feeding, or if it gets worse, think infection or internal disease. Watch for:

Bloating with raised scales (dropsy).
Bulging eyes (popeye), red streaks or ulcers.
Stringy white poop, weight loss, or not eating.

Over-the-counter "swim bladder" remedies often don't say what's in them and won't help if there's no infection. Medicating a fish whose real problem is water or feeding can make it worse. If you do medicate, use a hospital tank, remove activated carbon from the filter, follow the label, and finish the course. Take extra care with scaleless fish, plecos and other catfish, loaches, shrimp, snails and live plants: many medicines and salt are harder on them. Antibiotics need the right drug for the right bacteria, and many countries require a vet prescription.

When it's permanent. Some fancy goldfish are born with a squashed or deformed swim bladder, and some fish are left with damage after an infection. These fish can live for years with help: a bare-bottomed tank, shallow water, hand-feeding, and gentle tankmates. If a fish is in constant distress and can't eat, talk to a vet about humane euthanasia.

Products that help

Water test kit (liquid or strips): checks ammonia, nitrite and nitrate, the first things to rule out.
Sinking pellets or gel food: stops fish gulping air at the surface.
Frozen daphnia or brine shrimp: soft, easy-to-digest food for recovery.
Hospital tank or breeder box: keeps a struggling fish safe and lets you lower the water level.
Floating plants or a betta leaf hammock: resting spots near the surface.
Thermometer and reliable heater: steady temperature helps digestion.
Keep on hand: dechlorinator, a siphon, and a spare bucket for water changes.

How to prevent it

Feed small amounts, once or twice a day. Most fish need far less than you think.
Choose sinking food for fancy goldfish, or soak dry food before feeding.
Keep nitrate low with regular water changes. See how to clean a fish tank.
Match the temperature of new water at every water change.
Buy fancy goldfish from good breeders, and avoid fish that already struggle to swim in the shop.

Why it happened

Most often a full or gassy gut presses on the swim bladder after overfeeding or gulping floating food. Other causes include poor water, a sudden temperature drop, a deformed body shape, injury, and bacterial infection or internal disease. Veterinary sources note that when the swim bladder itself is diseased, the outlook is often poor.

When to get help

See a vet who treats fish if the fish hasn't improved in a week, if the problem keeps returning, or if there are other signs such as bloating, raised scales, bulging eyes or red sores. A vet can X-ray the fish, which is the best way to see the swim bladder, and can prescribe the right medicine if needed.

In the game

Multiple Tank Syndrome doesn't have a swim bladder card yet. The closest card is "Dropsy", another illness where a swollen belly is the warning sign.

Sources

WikiVet. Buoyancy disorders.
Aquatic Veterinary Services (Dr Jessie Sanders). Top 5 most common goldfish diseases.
injaf.org. Fancy goldfish and swimbladder/buoyancy problems.
Merck Veterinary Manual. Management of aquarium fish.