64 June 2012 traction and smooth muscle migration. Extracellular and membrane bound Hsp, especially Hsp70, are involved in binding antigens and presenting them to the immune system. The principal heat shock proteins that have chaperone activity belong to five conserved classes are Hsp33, Hsp60, Hsp70, Hsp90 and Hsp100 and the small heat shock proteins (sHsps). Although the most important members of each family are listed in Table 1, some species may express additional chaperones, cochaperones and heat shock proteins not listed. Tertiary Stress Response Chronic exposure to stressors provokes tertiary stress responses that result in a number of pathological changes and reduction in reproductive success, depression of growth and decrease in disease resistance. The tertiary stress response represents whole animal and population level changes associated with stress. In the whole animal, stress impairs growth, parrsmolt transformation, spawning success, migration behavior and spawning, and increased disease incidence. At the population level, stress acts to reduce intrinsic growth rate, recruitment, compensatory reserve, productivity, and altered community species abundance and diversity. Overall, when fish are exposed to an environmental stressor, a hierarchy of responses is initiated and, if the stress is sufficiently severe or long lasting, successively higher levels of biological organization are affected. Criteria for Identification of Stressed Fish The behavioral response is one of the immediate signs of stressed fish. Food acquisition, predator avoidance, prey capture, migration and habitat preference are critical to survival. Most physiological and environmental changes and handling can induce variations in fish behavior. Alterations of behaviors may take minutes to weeks to return to pre-stress conditions, depending on the nature and magnitude of the stressor. Behaviors that are most important to the survival of the organism tend to return to normal in the shortest time. Appropriate behavioral responses to the perception of a stressor will lessen the potential magnitude of that stressor and will increase chances of survival for that individual. Methods of monitoring and quantifying behavioral responses are potential alternatives for assessing stress from disease, water pollution and toxic materials in water. Some of the important visual criteria to identify stressed fish are schooling behavior and fish physical distribution, swimming behavior, darkening of body color, mucus secretion and feeding activity. Swimming. Estimation of swimming ability can provide a sensitive index to general stress in fish. Examples of altered swimming patterns include swimming into shallow water, swimming lethargically at the surface, lying listlessly on a pond or tank bottom, floating downstream or swimming erratically. Critical swimming speed and the length of time a certain swimming velocity can be maintained can also be used as indicators of stress. Respiration Rates (opercular beats). Respiration rate is a useful indicator of stress in fish. The difference between resting and active metabolism can be quantified simply by counting breaths (opercular beats) per minute or, more precisely, by measuring respiratory gases. Respiratory movements and oxygen consumption provide a measure of toxicological stress. Caution in Using Indicators of Stress There are many potential applications of the stress response. Features of physiological and cellular stress responses can be used to identify fish in intensive aquaculture that are in a stressed state. To make a reasonable interpretation, it is essential the baseline of any variable be established for species, season and any other factor that can influence the measured variable. Heat shock proteins represent a potentially convenient biomarker for several reasons. They may be measured when the blood volume is very small. They may be used when other indicators of stress are not available or well established. Hsp70 does not change in response to handling in fish. However, conditions that may occur in intensive aquaculture, such as anaesthesia, formalin exposure, hypoxia, hyperoxia, capture, crowding, food deprivation and cold shock do not affect Hsp70 in Atlantic salmon (Salmo salar). Thus, stress can exist when the measured variable does not change or have patterns that are not obvious without a baseline reference. Stress Mitigation Methods One of the most promising areas of research is the development of strategies to reduce stress on fish during various aquaculture practices. There are two approaches to mitigating stress: non-chemical (biological) and chemical. Non-chemical. Water quality is defined as the suitability of water for the survival and growth of fishes and water quality management is implementation of techniques to bring water quality to a desirable level for good growth and survival of fish. This includes management of water temperature, dissolved oxygen, alkalinity, pH, ammonia and turbidity. Chemical. These methods includes dietary supplementation of protein, vitamin C and vitamin E, L-tryptophan and lactoferin. Summary In aquaculture production, animals are exposed to many physical, chemical and biological stressors. Exposure of animals to stress elicits a cascade of physiological and biochemical changes characterized as primary, secondary and tertiary stress responses. Stress can be mitigated by biological and chemical methods. Notes 1Laboratory of Aquaculture & Artemia Reference Center, Ghent University, Belgium 2Central Institute of Fisheries Education (Deemed University), Mumbai, India 3College of Fisheries, CAU (I), Lembucherra, Tripura, India *Corresponding author: debtanu08@ gmail.com, Mobile- +32488191632
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