What the Swim Bladder Does
The swim bladder is a gas-filled organ that controls buoyancy. When working correctly, it lets fish hover at any depth without effort. When malfunctioning, the fish floats uncontrollably to the surface, sinks to the bottom, or swims sideways or upside down.
Fancy goldfish are uniquely vulnerable because their compressed body shape squeezes the swim bladder against organs and intestines.
The Three Main Causes
1. Constipation. The most common cause. A backed-up gut presses against the swim bladder. Symptoms: stringy white poop or no poop, swollen belly, struggling at the surface.
2. Gulped air from floating food. Common in fancy goldfish that strain at the surface. Causes air pockets in the gut that distort buoyancy.
3. Bacterial infection. Less common but serious. Usually triggered by poor water quality. Symptoms include reddened scales, lethargy, refusal to eat.
First-Line Treatment — The Pea Method
For constipation-related cases (90% of incidents), the proven home remedy is fasting plus shelled peas. Skip food for 2–3 days, then offer 1–2 thawed frozen peas with the shells removed (squeeze peas out of skins). Peas provide gentle fiber that flushes the gut.
Continue 1 pea per day for a week alongside small portions of normal food. Most cases resolve within 7–10 days.
When to Use Medication
If symptoms persist after 2 weeks of dietary correction, suspect bacterial infection. Treat with kanamycin or Maracyn 2 in a quarantine tank, following package directions. Bacterial swim bladder disease is harder to cure than constipation but still treatable if caught early.
Prevention
Use sinking pellets only. Soak floating pellets before feeding. Include 2–3 vegetable meals per week. Fast one day per week. Maintain water quality — bacterial swim bladder is almost always a water quality failure.