Gas bubble disease


A typical symptom of Crytobia is blindness, most noticeably fish swimming into objects.
Hanging at surface
Fish stays at water surface all the time.
Hyperaemia - fin base only
Excess of blood at base of fin.
Fish constantly rubs or scratches itself against any object available.
Sits on bottom
Fish sits still in upright position, on the bottom of tank or pond.
Spasms - convulsions
Fish appears to be having a fit, jerking and twisting abnormally.
Very agitated
Fish rushes around the tank or pond in an abnormal manner.
Skin petechiae
Small red spots on the skin.
Gas bubbles under head area
Gas bubbles are lodged under the skin of the head area of the fish.
Small fine air bubbles
Skin shows "trapped" tiny air bubbles caught or lodged on skin.
Fish jump out of water
Fish periodically leap above water surface trying to get air.
Listless and lethargic
Fish moves very lazily in water, much less than normal, lacks interest.
Milky patches on fins
Cloudy patches are scattered over the fin tissue.
Distal part of fins lose colour
Upper parts of fins lose their natural colour.


Caused by supersaturation of gases in the water. This is helped by sudden rise of the temperature. Can cause also a change in pH.
Causes are both artificial environmental & natural. Artificial causes :- Dams, Thermoelectric Power plants, Thermonuclear Stations, all forms of generating stations, plunge pools at base of dam spillways, water pumps, water intake pipes, transport of fish in airplanes, or ground transport.
Natural causes:- Melting snow, warming of surface water, rapid changes in barometric pressure.


Some lesions & disease, are reversible when gas levels are reduced below 103-106%. Fish exposed to supersaturated water at ~ 103% TDG are stressed & may later develop other conditions, i.e. fin rot, tail rot, coagulated yolk, bacterial diseases etc. Disease reversal also occurs in fish exposed to lethal gas levels (~ 120%), providing lesion development is not permanent ( blindness ). Fish in acute conditions frequently die without exhibiting external lesions. In sublethal supersaturation levels, external lesions & gas bubbles are more extensive because the fish have longer exposure to the gases before death.


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Effectively designed gas supersaturation controls must be tested & provided at the inception of any project which will affect water temperatures & pressures.


Dr. Hauck, Kent
Fish Pathologist
Utah Dept. of Aquaculture
Salt Lake City  UT.   USA


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