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stress

Definition

A state produced by any environmental factor which extends the normal adaptive response of an animal, or which disturbs the normal functioning to such an extent that the chances of survival are significantly reduced. Stress can be acute or chronic. An acute stress is one of short duration, minutes or hours, in which the time course of the response of the first outlasts that of the stress. Chronic environmental stresses are continuous forms of stress, from which, under aquaculture conditions, there may be no escape. Overcrowding, variable water quality, social domination, exposure to novel environments are all examples of chronic stress associated with fish farming. As a result, the HPI (hypothalamic pituitary interrenal) axis is activated, but in comparison with acute stresses here the blood cortisol levels may be elevated for prolonged periods (days, weeks). In many cases acclimation nevertheless occurs and the blood cortisol level returns to basal levels despite the continued stress.

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