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(22-10) Reduction of EROD activity with age in Atlantic tomcods from the St. Lawrence Estuary, Canada. Couillard, Catherine*,1, Légaré, Benoît1, Lebeuf, Michel1, Poirier, Guy2, 1 Department of Fisheries and Oceans, Maurice Lamontagne Institute, Mont-Joli, Quebec2 CHUL Research Center, Québec, Quebec ABSTRACT- Atlantic tomcods (Microgadus tomcod ) were collected at La Baleine, Quebec, in the St. Lawrence Estuary at the end of May or beginning of June on four consecutive years from 1998 to 2001. The St. Lawrence Estuary is the drainage basin for the industrialised sectors of the Great Lakes and the upper St. Lawrence River, and it receives relatively high loads of contaminants. A variety of biochemical bioindicators including the activity of ethoxyresorufin-O-deethylase (EROD) were used to investigate the relationship between fish health and the levels of persistent chlorinated contaminants in the liver. A 3 to 5 fold reduction of activity of EROD with age was observed repeatedly in female and male tomcods. The fish were captured several months after their spawning period (December-January) and the activity of EROD was not related to their gonadosomatic index. Exposure to inducing substances may differ among age groups as a result of differences in diet and/or behaviour. Alternatively, prolonged exposure to contamination may suppress cytochrome P450 1A1 activity. Fish liver had relatively high levels of chlorinated biphenyls and chlorinated pesticides. The levels of DNA adducts in the liver increased linearly with age and were not typical of those commonly associated with exposure to complex mixtures of polycyclic aromatic hydrocarbons. Increased prevalence of spinal deformities, preneoplastic and neoplastic liver lesions, jaw ulcers and poor body condition were observed in older fish. Experiments are underway to test different hypotheses explaining the reduction of EROD activity. Key words: EROD, Cytochrome P450 1A1, Atlantic tomcod, inhibition |
