UPTAKE AND RETENTION OF MIREX BY FISH MAINTAINED ON FORMULATED AND NATURAL DIETS IN LAKE-ONTARIO WATERS

Fish with no detectable levels of the contaminant mirex were grown in Lake Ontario waters under conditions simulating commercial aquaculture . Benthic black bullheads (Ameiurus melas) were grown in cages placed in a bay of the lake. Pelagic rainbow trout (Oncorhynchus mykiss) were grown in terrestrial raceways served with Lake Ontario waters. Contam inant-free fingerlings were reared to a large size on a commercial rat ion in these systems, which partially isolated them from the contamina nt-laden food web and bottom sediments. Black bullheads fed a mirex-sp iked, commercially prepared food had mirex concentrations that exceede d the U.S. Food and Drug Administration (FDA) action level of 0. 1 mug /g, significantly higher than concentrations in fish receiving the sam e commercial food without mirex. Ninety percent of fish receiving the unspiked ration had nondetectable levels of mirex (values below 0.002 mug/g). The 10% containing mirex had concentrations 94% below FDA acti on level. In the rainbow trout study, 97% of the fish had no detectabl e levels of mirex. This investigation demonstrated that bioaccumulatio n of the lipophilic contaminant mirex by fish cultured under simulated commercial conditions in Lake Ontario waters was not significant. The se findings have implications for commercial aquaculture, regulatory d ecisions, and health-conscious fish consumers in the Great Lakes Basin .