Changes in the swimming performance, behavior and physiology of juvenile chinook salmon (Oncorhynchus tshawytcha) after exposure to one, two or three acute handling stresses Public Deposited

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  • The performance of an organism or organismic subsystem is the result of the interaction between the performance capacity of the system and Its environment. Environmental conditions can stress an organism and thus affect it's performance. In this study, three whole organism performances were examined: critical swimming speed, fatigue time and response time to a sudden bright light. In addition, subsystem performances were examined by measuring changes in hematocrit and plasma levels of cortisol, glucose, lactic acid, osmolarity, sodium and potassium. Performance tests were made on juvenile chinook salmon stressed 0, 1, 2 or 3 times, with 1 or 3 h between stresses, and on fish allowed to recover 1, 3, 6, 12 and 24 h after each level of stress. A stress consisted of holding the fish in a dip net in the air for 30 sec. The physiological responses and the swimming tests were conducted on salt water adapted fish while the behavioral response was measured with fish in fresh water. Plasma levels of cortisol, lactic acid, osmolarity and sodium increased cumulatively following several acute handling stresses spaced I h apart, though each parameter returned to control levels in 6-12 h. Plasma glucose rose significantly by 1 h after the first stress and remained higher than control levels at all levels of stress and through 24 h after stress. Plasma potassium increased initially following one and two stresses, dropped below control levels within 1-6 h after the last stress, and then increased above control levels for the remainder of the 24 h. Following three stresses potassium was lower than controls initially and then was similar to the levels for one and two stresses throughout the rest of the 24 h recovery period. There was a decrease in hematocrit 3-6 h after each level of stress followed by a return to control levels within 12 h of the last stress. Critical swimming speed was measured by increasing the water velocity in a flow-through swim tube and noting the velocity at which each fish stopped swimming. Critical swimming speeds after handling were highly variable and no differences were found between stressed fish and unstressed fish at any level of stress or any recovery time. Fatigue time was measured as the time a fish can maintain position in a swim tube at a given constant water velocity (60 cm/sec). Following each fatigue test, fish were killed and blood samples were obtained. Unlike unstressed fish, which all fatigued within13 min, the times to fatigue of stressed fish varied with some fish fatiguing within a few minutes and some fish swimming the 60 min period. There was a depression in fatigue times immediately following one and three handling stresses spaced 1 h apart. Immediately after two stresses and with all groups given time to recover from stress, fatigue times were similar to or higher than for unstressed fish. Plasma levels of cortisol, glucose, osmolarity and sodium were higher in swimming fish than in non-swimming controls. Plasma concentrations of cortisol, glucose and lactic acid were all highly variable in fish following fatigue and no differences were found betweeen fish handled in a dip net and unhandled fish at any level of stress or any time after stress. Plasma osmolarity and sodium levels in fatigued fish immediately after one stress were higher than levels in unstressed fatigued fish. Plasma potassium was higher in fatigued fish than in unstressed fatigued controls at several time periods after one and three stresses. The behavior test consisted of exposing groups of salmon in fresh water to a sudden bright light and measuring the time it took each fish to reach cover. Unstressed fish reached cover within 15 sec. Stressed fish took longer to reach cover, with the greatest delay immediately after stress and a gradual decrease in response time with recovery from stress. Exposure to two and three consecutive stress with 3 h between stresses increased the response times and the recovery times indicating that the effects of stress were cumulative.
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