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.
Effectively designed gas supersaturation controls must be tested & provided at the inception of any project which will affect water temperatures & pressures.
Dr. Hauck, Kent
Utah Dept. of Aquaculture
Salt Lake City UT. USA