Studies of the correlation between stress-response, osmoregulation and thyroid physiology in rainbow trout, Salmo gairdnerii (Richardson)

Abstract

1. 1. Intraperitoneal injections of T 4 or thiourea lessened and increased, respectively, the hypernatremia evident in rainbow trout 48 hr after transfer from fresh water to 75% sea-water and both T 4 and thiourea injections reduced the stressor-induced elevation of plasma Cortisol levels evident in oil-injected controls after transfer to hyperosmotic media. 2. 2. Betamethasone blockade of cortisol secretion, or cortisol injections neither prevented the hypernatremia, nor altered the changes in hematocrit or plasma glucose levels evident in rainbow trout within 24 hr after transfer from fresh water to 75% sea-water. 3. 3. Plasma T 4 and T 3 levels tended to be higher in betamethasone-injected fish and thyroid hormone levels were elevated in betamethasone-injected fish after exposure to both osmotic and asphyxiation Stressors. 4. 4. Betamethasone blockade of cortisol secretion did not prevent the hyponatremia evident in rainbow trout after asphyxia and handling. 5. 5. The stressor-induced changes in plasma electrolytes and glucose levels and hematocrit differed in fish exposed to osmotic and asphyxiation Stressors, thus suggesting that these parameters may not necessarily be suitable indicators of a general stress response.