Methodology for implanting cortisol in Atlantic salmon and effects of chronically elevated cortisol on osmoregulatory physiology

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A method for achieving high physiological concentrations of cortisol in the plasma of Atlantic salmon (Salmo salar) is outlined. Cortisol was emulsified in vegetable shortening:vegetable oil (1 : 1). This mixture is fluid at 24°C and can be injected into the peritoneum where it solidifies into a slow-releasing cortisol implant. Three doses of cortisol implants were used: 25, 50 and 100 μg/g body weight. Salmon in the post-smolt stage were serially sampled in short-term (1 week) and long-term (1 month) experiments. There was significant variability in the vehicle-implanted control fish over time in both experiments. Except for day of the implant, there were no differences between the implanted controls and the non-implanted controls, indicating that the implant itself was probably not stressful. The medium dose (50 μg/g body weight) was found to elevate plasma cortisol within 1 day and to maintain plasma cortisol above vehicle-implanted salmon for as long as 1 month. The low dose was ineffective after 1 week and the high dose resulted in plasma cortisol concentrations above physiological levels. Exogenous cortisol increased the fluid uptake rate of the non-everted posterior intestinal sac after 1 month and increased the gill Na+ K+-ATPase activity after 1 week. These implants might be useful in allowing culturists to move salmon to sea cages at times outside the typical smolt window. © 1994.

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