Concentrations of Total Dissolved Solids Preferred or Avoided by Endangered Colorado River Fishes

Abstract

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 increases of TDS in the Colorado River system would degrade municipal, industrial, and agricultural water uses before these endangered fishes would be affected. Received November 1, 1982 Accepted June 5, 1983