Food habits of an Amargosa pupfish {Cyprinodon nevadensis amargosae) population inhabiting a thermal stream were examined at monthly intervals from January 1972 to April 1973. Little variation in foods eaten during the year was observed in the 218 specimens examined. The diet was almost entirely a mixture of blue-green algae and detritus. Invertebrates were only a minor component due to their scarcity in the stream. The smallest fishes consumed some invertebrates but this habit changed as the relative length of the digestive tract rapidly increased.