What causes a goldfish to swim abnormally?

Why Is My Goldfish Swimming Abnormally?
By Dr. Pornchanit Tuntijareonwiroj (Dr. Aoi)

Have you ever noticed that many goldfish brought in for treatment often exhibit strange swimming behaviors? Some may swim tilted to one side, float upside down, have their rear end sticking up or sinking abnormally. Others may lie motionless at the bottom of the tank, unable to swim like normal fish.

These symptoms are often signs of a condition called Swim Bladder Disorder, which involves a problem with the goldfish’s swim bladder—a key organ that controls buoyancy.

What Causes Swim Bladder Disorder?
When the internal organs—particularly the digestive tract—become enlarged, they can put pressure on the swim bladder. This may cause the bladder to malfunction or shift out of its normal position.

The main causes include:

Swallowing too much air while feeding – This can lead to excessive air accumulation in the digestive tract, pressing against the swim bladder.
Low-fiber diet – Poor-quality food with low fiber can cause constipation.
Overfeeding – Can lead to fat accumulation in the liver, causing it to enlarge and compress the swim bladder.
Enlarged internal organs or tumors – These can also put pressure on the swim bladder.
Systemic infections (Sepsis) – Bacterial infections in the bloodstream can affect internal organ function, including the swim bladder.

Treatment and Management
Adjust water temperature – Cold water slows digestion and can cause constipation. Keep the water at around 70–80°F (21–27°C).
Fasting – If the issue is due to overfeeding, withhold food for 3 days to allow the digestive system to return to normal.
Switch to high-fiber foods – Use goldfish food that contains at least 12% fiber to aid digestion.
Feeding adjustments – For fish that cannot feed properly, switch to sinking pellets or hand-feed to make eating easier.
Antibiotics – If a bacterial infection is involved, administer appropriate antibiotics such as fluoroquinolones, aminoglycosides, or beta-lactams.
Supportive devices – In severe cases, use a floatation device or life ring to help the fish maintain balance and improve its quality of life.