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Long-term changes, such as a poor or unsuitable environment, are handled with the same initial response – an alarm message to escape. However, if escape is impossible, the fish does not stop being stressed: it begins to adapt to the new environment as best it can.
At first, the fish’s body tends to overreact but, with time, it will adapt to reach the best possible balance – physiologically and behaviorally. Throughout the period of adaptation, the fish still prioritizes reacting to the new environment and remains stressed, so its immune system suffers and it is prone to disease. Adaptation normally lasts from four to six weeks.
However, if the fish continues to be in stressful conditions, such as a constantly deteriorating environment or endless bullying from aggressive tankmates, it continues to try to adapt and extends all the bodily responses as long as necessary. This reduces its chance of survival. In the worst possible situation, where adaptation to the new environment is impossible (such as putting marine fish in fresh water), the fish will exhaust itself fatally.
As a fishkeeper, it is extremely important to consider the effects of stress. Planning ahead, careful control of the environment and management of the fish population are fundamental basics in fishkeeping. Less stress means less disease.