A small ultrasonic fish tag is described, which is useful in studies of the game and pan fishes of freshwater lakes. The device emits a continuous signal of from 14 to 20 hr duration, at a frequency of 65 kilohertz. With the receiving equipment described, 37 white bass, Roccus chrysops (Raf.), have been successfully tracked in Lake Mendota for periods up to 13 hr. A study of the frequency of recapture of spawning white bass, marked with “dummy” transmitters in various ways, suggested that implantation in the stomach provided the more satisfactory tagging procedure. Of 672 fish tagged in various ways, 8.1% of those tagged externally, 6.2% of those with the tag implanted in the body cavity, and 18.8% of those with the tag placed in the stomach were recovered. In comparison, 17.5% of those marked with a hole punched in the soft dorsal fin were recaptured.