Impaired adrenocortical response to stress by brown trout, Salmo trutta, living in metal-contaminated waters of the Eagle River, Colorado

Brown trout, Salmo trutta, were collected from two sites contaminated with cadmium (Cd) and zinc (Zn) and one uncontaminated site. These fish were sub jected to a continuous confinement stressor in wire cages placed in the riv er (moderate stress) or in 5-gal. plastic buckets on land (severe stress). Plasma cortisol and corticotropin (ACFH) were determined for fish in bucket s by radioimmunoassay after 0, 1, 3, 12, or 24 h of confinement. Plasma cor tisol and ACTH levels of brown trout from both contaminated and uncontamina ted sites initially were the same and increased with time. However, the ris e in plasma cortisol was delayed significantly in fish residing in contamin ated sites, even though ACTH secretion initially was elevated compared with control trout. Furthermore, secretion of cortisol and ACTH by these fish d eclined significantly between 3 and 24 h of confinement. Fish from the unco ntaminated site responded more rapidly to confinement with increased cortis ol secretion and elevated levels of ACTH and continued to exhibit elevated levels of both hormones up to 24 h of confinement. Caged fish examined afte r 0, 3, 12, and 24 h of confinement exhibited similar plasma cortisol respo nses regardless of previous exposure to metals. These results suggest that the overall response to severe, short-term confinement stress by the hypoth alamo-pituitary-adrenocortical axis of fish chronically exposed to Cd and Z n was depressed and that these fish could not sustain the stress response a s readily as fish living in uncontaminated water. (C) 1999 Academic Press.