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Stress - Its Role in Fish Disease
Ruth Francis-Floyd  

What Causes Stress?
Stress is a condition in which an animal is unable to maintain a normal physiologic state because of various factors adversely affecting its well-being.

Stress is caused by placing a fish in a situation which is beyond its normal level of tolerance. Specific examples of things which can cause stress (stressors) are listed below.


Chemical stressors:
Poor Water Quality - low dissolved oxygen, improper pH
Pollution - intentional pollution: chemical treatments - accidental pollution: insect spray, spills
Diet composition - type of protein, amino acids
Nitrogenous and other metabolic wastes - accumulation of ammonia or nitrite


Biological stressors:
Population density - crowding
Other species of fish - aggression, territoriality, lateral swimming space requirements
Microorganisms - pathogenic and nonpathogenic
Macroorganisms - internal and external parasites


Physical stressors: Temperature: This is one of the most important influences on the immune system of fish. Light Sounds Dissolved Gases


Procedural stressors: Handling Shipping Disease Treatments Alarm reaction ("fight or flight" response) See Figure 1 .


Figure 1

Increases in blood sugar are caused by a secretion of hormones from the adrenal gland. Stored sugars, such as glycogen in the liver are metabolized. This creates an energy reserve which prepares the animal for an emergency action.

Osmoregulation is disrupted because of changes in mineral metabolism. Under these circumstances, a freshwater fish tends to absorb excess water from the environment (over-hydrate). A saltwater fish will tend to lose too much water to the environment (dehydrate). This disruption requires that extra energy be used to maintain osmoregulation.

Respiration increases, blood pressure increases, and reserve red blood cells are released into the circulation.

The inflammatory response is suppressed by hormones released from the adrenal gland.


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