Physiological Stress Responses in Wild and Hatchery-Reared Rainbow Trout

Stress-induced changes in plasma cortisol, glucose, and chloride were more extreme in wild rainbow trout Salmo gairdneri than in hatchery-reared fish subjected to confinement in a net and to electroshock. During 12 h of net confinement, plasma cortisol increased from resting levels of 10 ng/mL to 480 ng/mL in wild fish, and from 2 ng/mL to 155 ng/mL in hatchery fish. Plasma glucose was also higher in wild fish, increasing from 55 to 284 mg/dL, versus an increase from 58 to 196 mg/dL in hatchery fish. Plasma chloride decreased from resting levels of 132–135 meq/L to 53 meq/L in wild fish (and it continued a decline to 33 meq/L during the first 24 h after confinement), but only to 102 meq/L in hatchery fish. Both wild and hatchery-reared fish required more than 24 h after they were removed from the net to recover resting levels of plasma constituents. Plasma concentrations of cortisol, glucose, and chloride were less altered in response to electroshock than they were in response to net confinement. One hour after galvanonarcosis, plasma cortisol concentrations in wild fish peaked at 234 ng/mL and remained moderately elevated for 4 d; cortisol in hatchery fish peaked at 70 ng/mL within 0.5 h of the electrical stimulus and then returned to resting levels within 1 h. No substantial changes in plasma glucose or plasma chloride occurred in either the wild or the hatchery-reared rainbow trout after galvanonarcosis.