| Summary: | The flannelmouth sucker (Catostomus latipinnis) is one of the few native fish that persist in the lower Colorado River basin. Cold water discharged below Glen Canyon Dam may impair swimming ability of age-0 flannelmouth suckers. Reduced swimming ability may increase predation and restrict flannelmouth suckers to low velocity areas. I conducted laboratory tests to quantify reduction in swimming ability of age-0 flannelmouth suckers due to cold water and to evaluate effects of reduced swimming ability on predation. Flannelmouth suckers 25 to 115 mm TL were subjected to swimming performance tests at 10, 14, and 20° C. At 10°C, swimming ability was an average of 40% lower than at 20°C. Age-0 flannelmouth suckers acclimated to 20°C were introduced individually into tanks containing a single rainbow trout (Oncorhynhcus mykiss) at 20 or 10°C. Rainbow trout attacked more often at warm temperatures, but were more likely to capture prey at cold temperatures.
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