Cortisol treatment improves the development of hypoosmoregulatory mechanisms in the euryhaline rainbow trout, Salmo gairdneri

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Abstract
The effect of cortisol on osmoregulatory parameters was studied in rainbow trout, (Salmo gairdneri), kept in freshwater (FW) and/or transferred to seawater (SW). Repeated injections of 20 µg cortisol/g fish stimulated gill and gut Na+/K+-ATPase activity and reduced plasma Na+ and Cl− levels after 2 weeks of treatment in FW-adapted fish. Cortisol doses of 0.05 and 1.0 µg/g were without effect. Repeated injections of 10 µg cortisol/g stimulated gill Na+/K+-ATPase activity and reduced plasma Na+ and Cl− levels in fish in FW, and significantly improved ion regulation after their transfer to 28SW. Higher doses of cortisol (10 and 20 µg/g) induced hyperglycemia, whereas low doses (0.05 and 1.0 µg/g were without effect or induced hypoglycemia. Plasma glucose levels decreased in cortisol-treated fish transferred to SW, whereas transient hyperglycemia was seen in the control fish.

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