Electric stealth through bidirectional signal suppression in electric eels and their knifefish prey

Animals that use signal-based active location systems-electrolocation and echolocation-emit self-generated signals during foraging to sense their surroundings, but these signals are conspicuous to predators and prey. How such signals are modulated to balance sensory sampling against detection risk remains poorly understood. Both electric eels (Electrophorus) and their weakly electric knifefish prey are electroreceptive and generate electric organ discharges (EODs) that are essential for nocturnal foraging yet mutually detectable. Using autonomous electric-signal loggers in an Amazonian stream, we recorded signaling interactions between wild electric eels and knifefish. We found that both predator and prey temporarily reduce detectability by pausing electric signaling. Knifefish respond to eel EODs by evasive movements or by switching off their own EODs until the threat subsides. Laboratory-based playback experiments showed that EOD switch-off behavior is phylogenetically widespread among knifefish with pulse-type discharges and driven primarily by the low-frequency energy of eel EODs. Electric eels, in turn, frequently pause low-voltage electrolocation EODs during hunting, allowing them to approach electroreceptive prey with reduced detectability. During these silent intervals, eels forgo active electrolocation, likely relying instead on mechanoreception and passive electroreception. Electrolocation resumes immediately after emitting a high-voltage predatory burst-used for attack or probing-when prey localization outweighs the benefits of concealment. This bidirectional suppression of electric signaling parallels acoustic stealth dynamics in killer whales and their echolocating odontocete prey and mirrors alternating active-passive strategies used by human sonar and radar operators-revealing convergent solutions to the challenge of signals that are essential yet intrinsically conspicuous.