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each exposure period and tank revealed that selenium concentrations in muscle plugs at days 58, C~) 90, 120, and ] 53 were correlated with selenium in the diet (r= 0.657-0.759, P<O.OI, n=17-19), c., ,,~ ~'::'':la ,.;:;,. c.r) weights) in muscle tissue of adult females at day 153 and mean dietary concentrations was but not with selenium in the water. The relation between selenium residues (based on dry described by the follov.ing equation (r2=O.573, P<O.OI, n=19): Muscle plug selenium (ug/g) = 0.755+ O. I 84 x dietary selenium (ilg/g). To better examine selenium residue dynamics in these fish, the time course of selenium accumulation was plotted (figure 2). In contrast to females exposed to the control diets (treatments I and 2), selenium accumulation in muscle tissue appeared to reach a plateau at 90 days in females exposed to treatment 3 and at 120 days in females exposed to the treatments 4, 5, and 6. With the exception offish from treatment 6, muscle plug selenium concentrations at day 245 (90 days of depuration) were similar to those at day 153 (Table 11). These results indicated that the loss of selenium from muscle tissue was minimal after 90 days of depuration. Bioaccumulation factors (BAf, Rand 1995) for selenium in muscle tissue of individual fish at day ]53 (compared to the diet) were considerably lower than unity, ranging from 0.17 to 0.60 and were negatively correlated with dietary selenium concentrations (r=-0.82I, P<O.OI, n=19). Mean selenium BAf for females exposed to the control diets (0.55-0.57) were about twice as high as those for females exposed to the two selenium-fortified diets (0.21-0.29). Bioconcentration factors (i.e., ratio of tissue to water selenium concentrations) were not calculated because the accumulated selenium residues in muscle were due primarily to selenium in the diet. 44