User:Epipelagic/Thermal shock (fish)

Cooling tower of a nuclear power plant. Cooling towers from hydroelectric and nuclear power stations can produce temperature increases or decreases in rivers which result in fish kill.

Rapid changes in water temperature can stress fish, and in extreme cases result in fish die-offs. Stress occurs when a fish acclimated to a specific range of temperatures is exposed to a rapid increase or decrease in temperature. This can resulting in a cascade of consequences, possibly including death.

Thermal pollution

Thermal pollution is the degradation of water quality by any process that changes ambient water temperature.

A common cause of thermal pollution is the use of water as a coolant by power plants and industrial manufacturers. When water used as a coolant is returned to the natural environment at a higher temperature, the change in temperature (a) decreases oxygen supply, and (b) affects ecosystem composition. Urban runoff–stormwater discharged to surface waters from roads and parking lots--can also be a source of elevated water temperatures.

• water cooling

When a power plant first opens or shuts down for repair or other causes, fish and other organisms adapted to particular temperature range can be killed by the abrupt rise in water temperature known as thermal shock.

• Experts say cold weather likely cause of fish kill

Elevated temperature typically decreases the level of dissolved oxygen (DO) in water. The decrease in levels of DO can harm aquatic animals such as fish, amphibians and copepods.

• Overheated discharge water from nuclear power stations has resulted in significant fish kills in the past. Fish kills remain a problem for plants which use water for cooling, due to high volumes which pull fish into intake systems. Plants with cooling towers are more expensive, but allow for alleviating temperature effects.

• In common with Roseton and Indian Point Energy Center, the use by the Danskammer Generating Station of once-through cooling, in which river water was pumped in, used to cool the plant, then pumped out warm, dated to the 1950s and was responsible for large fish kills in the river.

• In the 1960s, the 1,500 megawatt Brayton Point Power Station was built by the New England Power Company in Somerset, Massachusetts at the north end of Mount Hope Bay. It has the largest capacity of any power plant in New England. For many years, the plant has relied on the waters of the bay as part of its cooling process. This has lead to severe thermal pollution, resulting in periodic fish kills.

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Bolivian fish kill 2010

Cold shock

Rapid decreases in water temperature can result in consequences for fishes called "cold shock". Cold-shock stress occurs when a fish has been acclimated to a specific water temperature or range of temperatures and is subsequently exposed to a rapid decrease in temperature, resulting in a cascade of physiological and behavioural responses and, in some cases, death. Rapid temperature decreases may occur from either natural (e.g. thermocline temperature variation, seiches and storm events) or anthropogenic sources (e.g. varied thermal effluents from power generation and production industries.

"Most of the research in the field of cold shock in fish has been carried out on rivers in temperate climates, rather than tropical ones. For example, fish in temperate rivers often die when a power station pumping warm water into a river suddenly shuts down. "

In 2010 unusually low temperatures resulted in the deaths of an estimated 6 million fish and thousands of alligators, turtles and river dolphins. Scientists described as event as the biggest ecological disaster Bolivia has known.

"Many fishermen lost their incomes and decomposing fish polluted rivers to the point where other sources of drinking water had to be found."

"Often, when cold weather causes fish deaths in lakes, the mortalities are directly due to hypoxia, when oxygen levels are too low to supply the animals' cells and tissues. This is because the colder surface temperatures can reduce mixing in the water column. Because the deaths occurred mainly in rivers,

Scientists suspect that the cold in the Bolivian die-off may have made the fish susceptible to infections."

Fish mortality is usually the result of several stressors acting together, and not the result of a single stressor. So, if cold shock or is being implicated in a fish die-off, something else is probably involved as well."