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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />METHODS <br /> <br />Age-O Colorado squawfish used in this study were <br />hatched in June 1988 at Dexter National Fish Hatchery (NFH), <br />New Mexico, and reared at willow Beach NFH, Arizona. After <br />fish had grown to desired lengths at willow Beach NFH, they <br />were transferred to the experimental chamber at Colorado <br />state University in three separate shipments. Total lengths <br />of fish upon arrival averaged 30.1 mm (small), 35.7 mm <br />(medium), and 44.0 mm (large). <br />Eighteen aquaria were housed inside an environmental <br />chamber. Each aquarium held only one size class of fish <br />(small, medium, or large). Aquaria were located on three <br />tiers of shelves, and fish size classes were randomly <br />assigned within each-tier. In the final experimental <br />set-up, I had three series of six aquaria, each holding <br />60 small fish, 45 medium fish, or 20 large fish. Initial <br />biomass in all aquaria was about equal. Fish were initially <br />held at 200 C before water temperature was lowered to the <br />simulated winter temperature (3-40 C) over a period of 24-48 <br />hours. Berry (1988) demonstrated that 40-day-old Colorado <br />squawfish subjected to either abrupt (5 min) or gradual (4-5 <br />h) temperature decreases of 150 C experienced very low <br />