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Experimental animals <br />Algae and rotifers <br />Monocultures of the freshwater algae Chlorella vulgaris (Carolina Biological Supply <br />Company, Burlington, North Carolina) were cultured using methods of Hoff and Snell (1989). <br />Algae were maintained in a series of batch cultures with five target exposure concentrations (0.0, <br />25, 50, 100, and 200 µg/L dissolved selenium). Algae were cultured in 4-L polyethylene bottles <br />containing 3 L of exposure water. From 600 to 900 ml of the algae culture were removed each <br />day for rotifer feeding. Consequently, the replacement rate of selenium in algae cultures ranged <br />from once every 3.3 to 5 d. <br />Monocultures of the rotifer Brachionus calyciflorus (Florida Aqua Farms, Dade City, <br />Florida) were also cultured in a series of batch cultures with five exposure concentrations using <br />methods of Hoff and Snell (1989). Rotifers were cultured in 20-L polyethylene bottles <br />containing 16 L of water. Each rotifer culture was fed algae from the corresponding selenium <br />treatment (e.g., rotifers in the 200 µg/L treatment were fed algae from the 200 µg/L treatment) <br />two or three times daily. Abundance of rotifers in batch cultures was quantified daily by <br />subsampling. On average, about 9% of the rotifer population in a culture was removed each day <br />for fish feeding. Replacement rate of exposure water in rotifer cultures was once every 2 d. <br />4 <br />