Cause Of Stress In Fish

Stress is the root cause of most diseases and health problems in fish especially in aquarium environments. The health of any living organism is directly related to levels of stress inflicted upon it. For fish this is a major problem because it cannot do anything to reduce or eliminate it, as they can only fight or succumb to it. Stress is present in the lives of all living things and can be described as the latent force that brings about physical, psychological and physiological change and adjustment (Stoskopf, 1993). Unfortunately the term ‘stress’ sometimes means the environmental alterations (stressors) itself and at times responses of the fish, population and ecosystem (Pickering, 1981). Stress can be extrinsic (environmental) or intrinsic

First phase of general adaptation syndrome is the stage of physiological alarm. During this stage, the effects of stressors (chemical or physical exposure) upset homeostasis of the organism. As the physiological system adjusts to compensate for specific effects from the mode of action of the contaminant, a host of non-specific homeostatic mechanisms are also induced in order to re-establish equilibrium. This stage may be associated with a loss of appetite, loss of equilibrium, locomotion and behavioural changes. Advantage of behavioural response is the integration of biochemical and physiological processes that reflect at higher levels of organization with ecological relevance. This rapid response reflects a defence mechanism protective against further exposure and potential for relocation of fish (Hellou, 2011). Sometimes fish leave the impacted habitats and migrate to unstressed areas. Second phase of the general adaptation syndrome is stage of resistance. This stage occurs when physiological adaptation to stressors has been accomplished. During this stage, compensating for the effects of chemical stressors becomes part of the normal cost of living for an exposed animal. This stage is associated with increased metabolic rate as most organisms are not adapted to energetic costs of compensating for anthropogenic stressors. Contaminant effects can be compensated, if the stressor is of sufficient magnitude and is applied for a sufficient length of time. Third phase of the general adaptation syndrome is the stage of exhaustion. During this stage, cumulative effects of long-term exposure to sub-lethal stressor result in premature death of the individuals. In case of chemical stressors, mortality occurs because the physiological system responsible for compensating for toxic effects becomes exhausted and shuts down. Exhaustion occurs because the physiological system is