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Abstract
Stress is an event that most animals experience and that, induces a number of responses involving all three regulatory systems, neural, endocrine and immune. Fish cultures are especially at risk to the adverse effects of stress. Blood chemistry and hematological measurements can provide valuable physiological indices that may offer critical feedback on different stressors. Blood samples were collected from the caudal vein of Carassius carassius after subjected to stressors and parameters such as plasma cortisol and glucose levels were estimated. Also, immunological response through neutrophil/lymphocyte ratio were evaluated. The responses of C. carassius to stress were characterized by rapid and transient significant increases in glucose, hemoglobin, hematocrit, as well as an equally dramatic but delayed increase in cortisol levels. High ratio of neutrophils to lymphocytes (N: L) in blood fish were found, which reliably is related with high glucocorticoid levels. Our results strongly indicate the close relationship between stress hormones and neutrophil/lymphocyte ratio, concluding that N: L ratio and its relation with glucocorticoid hormones can provide a reliable method to study responses of fish to stress.
Key words: stress, plasma cortisol, glucose, immunological response, neutrophil, lymphocyte.
1.Introduction
Stress is defined as "the nonspecific response of the body to any demand made upon it" [39]. The response to stress is considered an adaptive mechanism that allows the fish to cope with real or perceived stressors in order to maintain its normal or homeostatic state [7]. Stress can be considered as a state of threatened homeostasis that is re-established by a complex suite of adaptive responses [9] . The stress response applies to a wide range of physiological mechanisms, including gene and protein changes, metabolism, energetics, immune, endocrine, neural and even behavioral changes that will first try to overcome that situation and then compensate for the imbalances produced by either the stressor or the consequences generated by the first array of responses. With these reactions the animal tries to avoid dangerous situations and the risk to life and body integrity, and subsequently to cope with the allostatic load produced by the stressor and reintegrate the balance throughout physiological systems in order to regain homeostasis [43]. Physiological responses of fish to environmental stressors have been grouped broadly as primary, secondary and tertiary [7]. Primary responses, which...