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experimental unit was an aquarium. Forty-five 76-L aquaria (30 x 75 x 32 cm <br />high) were housed within the same room. Cool-white fluorescent lamps were the <br />only source of illumination, and a 12:12-h light:dark photoperiod was <br />maintained. <br />Water was supplied by a well on the Colorado State University campus and <br />had the following characteristics: dissolved ,oxygen, > 6.1 mg/L; pN, 8.2; <br />temperature, 20 ± 1 °C; alkalinity, 237 mg/L as CaC03; hardness, 344 mg/L as <br />CaC03; and specific conductance, 720 µS/cm. The bottom of each aquarium was <br />covered with approximately 2 cm of washed sand. Each aquarium was aerated <br />continuously with a single airstone and water was added periodically to <br />maintain a depth of 24 cm. <br />Zooplankton abundance levels were based on results of field studies and <br />encompassed a realistic range of zooplankton densities (S. J. Grabowski and <br />S. D. Hiebert, unpublished report). Zooplankton were collected from Fossil <br />Creek Reservoir (Larimer County, Colorado) with an 80-µm-mesh plankton net. <br />Zooplankton were transferred to the laboratory where they were quantified by <br />subsampling and a stock was prepared by diluting to a target density. <br />Aliquots of stock were delivered to aquaria twice daily to obtain 2000 <br />zooplankton per aquarium per feeding (26 zooplankton / L). Feeding-regime <br />levels (32, 80, and 200 zooplankton•fish~~•day~~) were obtained by manipulating <br />number of fish per aquarium rather than number of zooplankton. For example, <br />the 32 zooplankton•fish-~•day~~ treatment was obtained by delivering 2000 <br />zooplankton twice daily into an aquarium containing 125 fish. Numbers of fish <br />per aquarium corresponding to 80 and 200 zooplankton•fish-1•day~~ were 50 and <br />20, respectively. This procedure allowed manipulation of zooplankton relative <br />8 <br />