We conducted laboratory tests to evaluate the effects of an abrupt 10°C decrease in water temperature on ability of age-0 flannelmouth suckers (Catostomus latipinnis) to escape predation by rainbow trout (Oncorhynchus mykiss). Juvenile flannelmouth suckers (58 mm mean total length) were maintained at 20°C and introduced individually, without acclimation, into tanks containing a single adult rainbow trout (246 mm mean total length) at 10 or 20°C. Rainbow trout attacked suckers more often at 20°C, but were more likely to capture them at 10°C. Age-0 flan-nelmouth suckers experience an abrupt temperature decrease when they exit warm tributaries and enter cold hypolimnetic water released from Glen Canyon Dam on the Colorado River. This temperature change might increase susceptibility of young flannelmouth suckers to predation by rainbow trout, which are abundant in the Colorado River in Glen, Marble, and Grand canyons.