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(18-43) Effects of municipal sewage effluents on the immune and thyroid functions of rainbow trout (oncorhychus mykiss). Fournier, Michel*,1, Escarné, Régina1, Cyr, Daniel1, Finnson, Ken1, Marcogliese, David2, 1 INRS-Institut Armand-Frappier, Pointe-Claire, Québec, Canada2 St-Lawrence Center, Environment Canada, Montréal, Québec, Canada ABSTRACT- Municipal sewage effluents contain a complex mixture of chemical substances known to disrupt immune and endocrine functions. In this study we determine the effects of municipal sewage effluents on the immune and thyroid function of the rainbow trout (Oncorhynchus mykiss). Trouts were exposed to five dilution 0.001/30, 0.01/30, 0.1/30 and 1/30 of Montreal municipal effluent for a period of 15 or 45 days. Immunological function was assessed on 15 trouts from each group and the remaining fish were challenged with Aeromonas salmonicida, responsible for furunculosis. Phagocytosis, by kidney macrophages, and lymphocyte proliferation were measured. Thyroidal status was assessed by measuring hepatic T4 5'-deiodinase activity. For the 15 days exposure, both number and phagocytic activity of macrophages were significantly increased in trout exposed to lower levels of effluent relative to the control group. However, this response was not observed in trouts exposed to higher effluent concentrations suggesting a possible immunosuppressive effect. Concanavilin A (Con A) stimulation of lymphocyte was decreased in trout exposed to all effluent concentrations relative to the control group. Pokeweed mitogens (PWM) stimulation of lymphocyte proliferation was not significantly different among all groups tested. These data suggests that certain sub-populations of T-cells are stimulated while others are suppressed by effluent exposure, even at low effluent concentrations. For the 45-days exposure group, both number and phagocytic activity of macrophages were significantly decreased in trouts exposed to 0.01/30 effluent dilution. However, phagocytic activity was significantly higher in trouts exposed to 0.1/30 and 1/30 dilutions. Moreover, cells stimulated with PWM were significantly lower in trout exposed to 1/30 effluent dilution. Also, control trouts were more sensitive to A. salmonicida exposure and resistance increased with increasing effluent concentrations in both 15- and 45-day exposure groups. Hepatic T4 5'-deiodinase activity in control and effluent exposed trout were not significantly different. This study is the first documented evidence of in vitro alteration of immune function in fish caused by municipal effluents. Supported by CNTC and FAQDD. Key words: Thyroid hormones, Trout, Immunotoxicology, Municipl sewage |
