Stress in Fish

Stress in fish is an habitual, undesirable aspect of production. Stress results from biotic and/or abiotic challenges that act in changing or modifying the animal's natural or homeostatic state. Common fish stressors involve alterations in the fish's immediate environment such as:

• Chemical changes - contaminants, low oxygen and acidification
• Physical changes - handling, capture, confinement and transport
• Perceived changes - startling or predators

The above stressors are categorised as either acute or chronic depending on their duration and frequency. Acute fish stressors are events which the animal experiences for a short period of time such as handling. Chronic fish stressors are defined as a constant or recurring exposure that causes a prolonged physiological response. Fish stressors of both types have severe negative effects on the animal's growth and health.

The Physiological Response to Stress in Fish

Generally, stress in fish is a non-specific response classified as three distinct responses:
Primary responseThe primary response is characterised by the activation and the secretion of the hormones, corticosteroids (cortisol) and catecholamines, into the blood.

Secondary responseThe release of hormones triggers the secondary response which involves the release of glucose into the blood for energy production, followed by increases in heart rate, gill blood flow and metabolic rate which causes changes to blood lactate and hematocrit.

Tertiary responseChanges in blood physiology ultimately cascade into a whole body change or the tertiary stress responses. Changes associated with the tertiary stress response include reduced growth rate, decreased disease resistance, altered behavior and reduced survivability.

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