Multiple Acute Disturbances Evoke Cumulative Physiological Stress Responses in Juvenile Chinook Salmon

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Abstract
The corticosteroid and hyperglycemic stress responses to multiple acute disturbances were cumulative in juvenile chinook salmon Oncorhynchus tshawytscha. This was demonstrated by the stepwise pattern of increased plasma cortisol and glucose concentrations in fish subjected to a 30‐s handling stress applied repeatedly at 3‐h intervals over 6 h. The accumulation of physiological stress responses was substantiated by the resultant combined effects of these repeated disturbances on changes in concentrations of plasma lactate and of ionic sodium and potassium, and on the rate of decline of hepatic glycogen concentrations, all of which were greater than those that followed a single handling. Healthy fish appeared more able than diseased fish to elevate plasma cortisol after each of the three successive disturbances, but plasma glucose concentrations following the repeated handlings were higher in the unhealthy fish. As judged from plasma cortisol and glucose responses in fish subjected to a single 30‐s stress at four different times in the day, there was little diurnal difference in sensitivity or responsiveness to handling.