Gas Bubble Disease (Gas Supersaturation) in Fish: A Guide

Gas bubble disease is a non-infectious condition caused by gas supersaturation of water. Dissolved gases form emboli in fish tissues, causing injury and mortality.

Overview

Gas bubble disease is a non-infectious, environmental condition rather than a disease caused by a pathogen. It occurs when water becomes supersaturated with dissolved gases, meaning the total dissolved gas (TDG) exceeds 100% of saturation. Although oxygen or carbon dioxide can contribute, the gas most often responsible is nitrogen. When fish live in supersaturated water, the excess gas comes out of solution inside their blood and tissues, forming gas emboli that block small vessels and injure the animal. The condition can affect any aquatic species and is a recognized risk in hatcheries, aquaria, and aquaculture systems.

Causes

Well, spring, or deep-water supplies naturally high in nitrogen or carbon dioxide
Cavitating pumps that draw in and pressurize air
Leaks in plumbing on the intake (suction) side, which let air be drawn in and forced under pressure through the pump
Rapid heating of cold water, which lowers gas solubility and drives gas out of solution
Excessive turbulence or intense photosynthesis (algal blooms) that supersaturate the water

Clinical signs

Exophthalmia (bulging eyes)
Tiny gas emboli (bubbles) visible in the fins, corneas, skin, and gills
Gas emboli within the gill capillaries, which is diagnostic
Buoyancy problems and abnormal swimming
Acute, catastrophic or chronic mortality; eggs and larvae are especially vulnerable

Diagnosis

Diagnosis is based on finding gas emboli in the tissues, particularly within the gill capillaries, which is considered diagnostic. The underlying cause is confirmed by measuring the total dissolved gas in the water with a saturometer, which measures all dissolved gases and is the best tool for direct detection of supersaturation.

Prevention and correction

Because the condition is environmental, the priority is to find and fix the source of supersaturation and to drive the excess gas back out of the water before it reaches the fish.

Identify and repair the cause, such as an intake-side air leak or a cavitating pump
Vigorously aerate or degas incoming water to volatilize and off-gas the excess gas
Use degassing methods such as packed columns or aeration towers, especially for well water
Aerate water before it contacts fish, allowing it to equilibrate to normal saturation
Where appropriate, hold fish in deeper water, where higher pressure increases gas solubility