- Genetic, ontogenetic, and environmental factors modified characteristic interrenal and glycemic responses to stress in juvenile salmonid fishes. During continuous confinement stress, plasma cortisol rose more quickly in chinook salmon, Oncorhynchus tshawytscha, acclimated to high rather than medium or low temperatures; hyperglycemia following either acute or chronic stress was also highest in this group. When chinook salmon were subjected to three handling stresses, separated by 3-h intervals, increases of plasma cortisol, glucose and lactate and decreases in plasma sodium were cumulative. Healthy chinook salmon appeared sore able than diseased fish to elevate plasma cortisol after stress, but post-stress plasma glucose was higher in the unhealthy fish. Glycemic responses to stress in chinook salmon were related to diet type and to fasting. When rainbow trout, Salmo gairdneri, were exposed to pH 4.7 and then handled, the post-stress plasma cortisol elevation was more than twice that in those at ambient pH. Rainbow trout subjected to an acute disturbance daily for 10 wk exhibited habituation, evident from plasma cortisol and glucose levels after handling that were about one half of those in previously unstressed fish. The interrenal. response to handling in coho salmon, Oncorhynchus kisutch, increased twofold during the normal period of smoltification. A comparison of chinook salmon, coho salmon, rainbow trout and brook trout, Salvelinus fontinalis, subjected to identical handling stresses, suggested that there were species and stock differences affecting the megnitude of plasma cortisol elevations.
Rainbow trout fed with cortisol-treated feed exhibited reduced growth, condition factor, liver glycogen and circulating lymphocytes, and higher plasma glucose and hemetocrit. The plasma
cortisol elevation following handling was completely abolished in the cortisol-fed trout, indicating that continuous negative feedback of cortisol eliminated the fish's ability to initiate an interrenal stress response. When forced to swim, seen oxygen consumption rate in
stressed steelhead, Salmo gairdneri, was about twice that in unstressed fish and individual rates were positively correlated with please cortisol elevations. The metebolic cost of this stress
was estimated to reduce the energy available for other performance components within the fish's scope for activity by about one quarter.