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 sample 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. In turn, electric eels 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.