Buoyancy Disorders

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Also known as: Swim Bladder Disorders


In fish, buoyancy is controlled by the amount and distribution of gas within the body. This is primarily found in a gas-filled buoyancy organ, the swim bladder. Some fish control the amount of gas in their swim bladder by swallowing and forcing air down a patent duct connecting the oesophagus and the swim bladder. In other fish, gas is released from arterial blood by a vascular rete in the wall of the swim bladder to fill it.

Buoyancy disorders are quite common in fish, especially ornamental fish and goldfish. Some body conformations seem to predispose to swim bladder disorders, such as the short stout bodies found in Asian goldfish varieties.


Over-inflation of the swim bladder: chronic bacterial diseases, granulomatous disease, gas supersaturation, renal tumours

Displacement of the swim bladder: the posterior chamber of the swim bladder is easily displaced by masses including renal tumours and polycystic kidney disease. Torsion is also possible.

Fluid in the swim bladder: transudate or exudate, bacterial infections

Intestinal tympany

Rupture of the swim bladder: free gas in the retroperitoneal space

Clinical Signs

The condition is usually of sudden onset and fish will usually be found lying at the bottom of the tank (negative buoyancy) or floating at the surface (positive buoyancy).

Fish may also have an abnormal body posture, may roll to one side or be completely upside down. Some fish can present with their heads pointing downwards.

Exophthalmos may be present if there is a systemic disease.

Abdominal swelling, usually asymmetrical, may be present.

Fish that have been partly exposed to air for some periods of time may have skin lesions from desiccation or may have trauma from contact with substrate.


Clinical signs and presentation are characteristic of a buoyancy disorder.

Radiographs are invaluable in assessing the swim bladder and gas distribution in the fish. It enables a clear view of the swim bladder and the intestinal loops, and can provide information on kidney structure.

Ultrasonography is of little use for swim bladder disorders, but can identify other pathology and polycystic kidney disease.

Post-mortem examination usually enables a definitive diagnosis to be made, through tissue examination and culture.


Response to treatment is often poor as usually the underlying disease is severe. Euthanasia is usually indicated, but some treatments can be attempted if no other signs of disease are present.

Environmental management:

water quality should be improved through partial water changes
sodium chloride can be added to the water for freshwater fish
slightly altering the temperature may be beneficial
starving for 2-3 days to allow emptying of gas-producing contents in the bowel
crushed green pea fed daily to purge the intestinal contents

Medical therapy:

Proprietary products which claim to treat buoyancy disorders, ingredients are unknown and efficacy is variable
Antibiotics may be effective if bacterial infections are involved
Carbonic anhydrase inhibitors for over-inflated swim bladders to decrease gas accumulation


Flotation devices for fish with negative buoyancy, variable efficacy
Paracentesis of the swim bladder to deflate it temporarily, usually a shot-term effect
Surgical correction of a torsion or displacement: technically difficult and risky

Fish usually die or are euthanased and prognosis is poor if a buoyancy disorder is present.

Buoyancy Disorders Learning Resources
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Test your knowledge using flashcard type questions
Ornamental Fish Q&A 04


Hoole, D. (2001) Diseases of carp and other cyprinid fishes John Wiley and Sons

Roberts, H. (2009) Fundamentals of ornamental fish health John Wiley and Sons

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