Gas Bubble Disease

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Also known as: Gas Supersaturation


Gass bubble disease is associated with the supersaturation, with nitrogen or oxygen, of the water in which fish are kept. It occurs when the total pressure of gases dissolved in water is higher than the ambient atmospheric pressure.

In aquariums, causes include leaks in pumps or valve systems that can suck air under pressure or sudden temperature gradients. Fish transported by air may also develop gas bubble disease.

Heavy algal blooms have also been blamed, by producing more oxygen than can diffuse into the water which supersaturates the pond.

Most gas emboli are produced by excess nitrogen because oxygen is assimilated metabolically and thus less likely to form persistent bubbles. However, very high oxygen levels are dangerous.

When fish breathe supersaturated water, the excess gas can form emboli in various tissues. The severity of the disease depends on the number of gas bubbles formed and the tissues affected. Brain damage, behavioural abnormalities and death may all occur.

Clinical Signs

Acute gas bubble disease manifests as acute mortality and may occur in minutes. Eggs float to the surface and fish may show hyperinflation of their swim bladder, cranial swelling, exophthalmos, blindness, swollen gill lamellae, pneumoperitoneum or gass bubbles in the yolk sac. Up to 100% of fish may die.

Chronic gas bubble disease results in a few mortalities, hyperinflation of the swim bladder, emboli in the gastrointestinal tract and mouth, and secondary infections which can lead to higher mortality rates.


The clinical signs are suggestive but fish may die suddenly without apparent cause.

The presence of gas emboli is characteristic. Bubbles may be squeezed from a fin or gill clip whilst it is held underwater.

The total concentration of dissolved gas in the water source should be measured using a saturometer.

Post-mortem findings include internal gaseous accumulation in the swim bladder and visceral peritoneum.

Histology may reveal oedema of the secondary lamellae of the gills and occlusion of the large branchial vessels.


Any leaks or problems with the system should be dealt with promptly.

Treatment of the disease involves eliminating the excess gas in the water source.

This could involve aerating the water source to allow it to equilibrate with air.

A packed column degasser can be used to strip the excess gas from the water.

Fish that recover from an outbreak have a variable prognosis depending on the degree and the duration of supersaturation they experienced.

Gas Bubble Disease Learning Resources
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Test your knowledge using flashcard type questions
Ornamental Fish Q&A 22


Roberts, R. (2001) Fish Pathology Elsevier Health Sciences

Noga, E. (2010) Fish disease: diagnosis and treatment John Wiley and Sons

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