STRUCTURAL AND FUNCTIONAL IMPAIRMENT OF THE HYPOTHALAMO-PITUITARY-INTERRENAL AXIS IN FISH EXPOSED TO BLEACHED KRAFT MILL EFFLUENT IN THE ST-MAURICE RIVER, QUEBEC

The effects of bleached kraft mill effluent (BKME) on blood cortisol l evels and the morphology of the pituitary-interrenal axis were investi gated in two species of teleost fish, the northern pike, Esox lucius, and the yellow perch, Perca flavescens, sampled upstream and downstrea m from a pulp and paper mill on the St Maurice River, Quebec. Fish wer e acutely stressed by a standardized capture and sampling protocol at both sites, and their ability to elevate blood cortisol levels in resp onse to the capture stress was compared. Blood cortisol levels in fish from the upstream site (>100 ng/ml plasma) were higher than the level s in fish from the BKME site, and the pituitary corticotropes and the interrenal steroidogenic cells of the upstream fish were larger and ha d larger nuclei compared with cells from the downstream fish. The low blood cortisol levels in fish exposed to BKME were correlated to cellu lar atrophy within the hypothalamo-pituitary-interrenal (HPI) axis. Th e reduced ability to elevate blood cortisol in response to an acute st ress may be an endocrine dysfunction occuring in fish chronically expo sed to chemical stressors in their environment.