Fathead minnows (Pimephales promelas Rafinesque) were abundant in 9 of 10 prairie pothole lakes in south-central North Dakota, selected to represent extremes in salinity. Fathead minnows were found in lakes with mean concentrations of total dissolved solids during ice-free periods ranging from 385 to 7,036 mg/liter; no fish were found in North Lake George with a mean concentration of 23,489 mg/liter total dissolved solids.