Corticoid Stress Responses to Handling and Temperature in Salmonids

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Abstract
Plasma corticoid concentrations in juvenile chinook salmon (Oncorhynchus tshawytscha) netted and confined in a small live‐cage rose from approximately 100 ng/ml to about 500 ng/ml in 24 h, then fell to 250 ng/ml at 48 h. In juvenile chinook salmon dip netted into a bucket containing aerated water and sampled serially at 90‐s intervals, plasma corticoids increased from < 10 ng/ml to approximately 100 ng/ml in 20 min. In juvenile cutthroat trout (Salmo clarki clarki) acclimated to 13 C and subjected to a rapid increase in water temperature to 26 C, plasma corticoid concentration increased from about 20 ng/ml to 70 ng/ml in 25 min and remained elevated for more than 3 h. Juvenile cutthroat trout acclimated to diurnal temperature cycles (13–23 C) had no substantial changes in plasma corticoid concentration throughout the cycles. Juvenile cutthroat trout acclimated to 23 C had the same initial corticoid concentration as cutthroat trout acclimated to 9 C. When both groups were subjected to identical netting and confinement, the corticoid concentrations in fish from the two temperatures responded in a similar fashion until 70 min of confinement when trout from the warmer water failed to maintain increasing corticoid concentrations.