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Fish were grown in Lake Ontario water under conditions simulating commercial aquaculture and then analyzed for 10 priority organic contaminants. Black bullheads (Ameiurus meias) were grown in cages placed in a bay of Lake Ontario. Rainbow trout (Oncorhynchus mykiss) were grown in terrestrial raceways served with Lake Ontario water. Yearlings were reared on a commercial ration in these systems, which partially isolated them from the contaminant-laden food web and bottom sediments, to an average weight of 93 g for black bullheads (range, 31-220 g) and 213 g (29-558 g) for rainbow trout. Concentrations of contaminants in skinless fillets of both rainbow trout cultivated 6 months and black bullheads cultured 3.5 months in Lake Ontario waters were nondetectable or less than one-sixth the "action levels" defined by the U.S. Food and Drug Administration. Contaminant levels in rainbow trout were consistently less than concentrations observed in black bullheads. Of the 10 priority contaminants surveyed, 7 were nondetectable in rainbow trout and 3 were nondetectable in black bullheads. Concentrations of contaminants in both species were generally much lower than levels observed in wild fish from Lake Ontario. This investigation demonstrated that bioaccumulation of lipophilic contaminants by fish cultured under simulated commercial conditions in Lake Ontario was not significant. These findings have implications for commercial aquaculture, regulatory decisions, and fish consumers in the Great Lakes basin and elsewhere.