They generate charged fields around their bodies with trunk muscle tissue that has been modified by evolution into organic batteries. The power is controlled by a neural switch. Each time the switch turns on the field, individual fish sense the resulting power with electroreceptors distributed over their bodies. Perturbations caused by nearby objects, which cast electric shadows over the receptors, allow them to judge size, shape, and movement. Thus continuously informed, the fish glide smoothly past obstacles in dark water,
