Chapter 14: Stress and Acclimation
Gary A. Wedemeyer, Bruce A. Barton, and Donald J. Mcleay
The physiological systems of fishes can be severely challenged or “stressed” by a variety of biological, chemical, and physical factors. Knowledge of the tolerance limits for acclimation to the single or cumulative effects of such biotic and abiotic stress factors is an important part of the data base for species-habitat relationships needed for effective fishery resource management. The solution of problems ranging from prediction of the tolerance fish will have for proposed habitat alterations to evaluation of the effects on fish health exerted by modern intensive fish culture depends on such information.
It is well known that acute or chronic stress approaching or exceeding the physiological tolerance limits of individual fish will impair reproductive success, growth, resistance to infectious diseases, and survival. If the stress is severe or long-lasting, succeedingly higher levels of biological organization become affected. The cumulative effects of even sublethal stress factors may reduce recruitment to successive life stages and eventually cause populations to decline (Vaughn et al. 1984; Adams et al. 1985).
If terms are not used consistently, stress can be a confusing physiological concept. Stress was originally defined in general terms by Selye (1950) as “the sum of all the physiological responses by which an animal tries to maintain or reestablish a normal metabolism in the face of a physical or chemical force.” More specifically, stress in fish results from biotic or abiotic challenges or forces that extend homeostatic or stabilizing processes beyond their ability to control routine physiological processes (Esch and Hazen 1978). The term “stressor” and “stress factor” should be used to mean the force or challenge that elicits a compensatory physiological response (Pickering 1981). Thus, an environmental or biological challenge (stressor) that is severe enough to cause stress is one that requires a compensating response by a fish, population, or ecosystem. Acclimation may be possible if the compensatory stress response can reestablish a satisfactory relationship between the changed environment and the fish or higher-order biological system. However, the cumulative effects of even sublethal stress factors may eventually lead to deaths even though the factors may not individually exceed physiological tolerance limits (Donaldson 1981; Carmichael 1984; Barton et al. 1986). Thus, the tolerance limits for acclimation to multiple stress factors are determined in part by the cumulative physiological effects of the prior stressors.