Tracking individual spatial and activity-rest patterns in natural populations is challenging because it is seldom possible to monitor individual-specific traits continuously. The continuous emission of electric signals (EODs) by weakly electric fish provides a unique opportunity to do this. We present a cutting-edge technique, arrays of electrodes connected to low-cost amplifiers and tracking algorithm, to provide the individual identification of pulse-type weakly electric fish in the wild. Based only on EOD recordings of individuals of Gymnotus omarorum, we show that (1) there are more fish in core than in edge zones; (2) transitions into and out of the recording sites were more frequent at night, and (3) resident fish show robust nocturnal increases of EOD rate likely associated with daily variations of water temperature. This experimental approach can be extended to other species to improve our understanding of the behavior, ecology, and well-being of electric fish in natural environments.