Sustained Exercise Increases Plasma Growth Hormone Concentrations in Two Anadromous Salmonids

Abstract

Sustained exercise for 24 h at 1.5 body lengths per second (bl/s) resulted in a severalfold increase in the plasma growth hormone (GH) concentration of steelhead trout (Salmo gairdneri) and coho salmon (Oncorhynchus kisutch). Peak levels occurred 10 min postexercise and returned to basal levels within 4 h of exercise termination. GH levels exhibited a steady increase after the fourth hour of exercise and peaked at 24 h. Individuals exercised for 48 h did not exceed plasma GH levels of the 24-h peak.