Feeding by adult Rainbow Smelt (Osmerus mordax) is selective and varies with fish size, sex, and season. Intensity of feeding is lowered prior to spawning. Zooplankton is the major food, and we found no evidence of predation on the eggs or young of sport fishes. Fish were found in the stomachs of 11% of the females and 4.3% of the males and were mainly young-of-the-year smelt in summer and lake Emerald Shiners ( Notropis atherinoides) in winter and spring. Fish were eaten only by smelt of age groups I to V (156 to 204 mm in fork length) while crustaceans were the principal food of young-of-the-year smelt.