Juveniles (age 0-1) of three endangered Colorado River fishes were subjected to a gradient of total dissolved solids (TDS) to determine the concentrations that they preferred or avoided. Preferred and avoided TDS concentrations, respectively, for juveniles of each species were: Colorado squawfish Ptychocheilus lucius, 560-1,150 mg/liter and greater than 4,400 mg/liter; humpback chub Gila cypha, 1,000-2,500 mg/liter and greater than 5,100 mg/liter; and bonytail Gila elegans, 4,100-4,700 mg/liter and less than 560 mg/liter or greater than 6,600 mg/liter. Colorado squawfish and humpback chubs selected TDS concentrations that were similar to those in waters they now inhabit, but bonytails selected concentrations four times higher. Future [...]