Aquatic animals display a variety of modes and uses for electroreception. For best results, you're going to want an environment where electroreception is their primary means of both locating and identifying prey - as opposed to identifying targets by sight, then using electric signals at close range if the target is hiding. This would most likely be in extremely turbid waters where there is little available light.
Animals that use active electroreception - generating a low-level electrical field and measuring distortions in the field, similar to echolocation or active sonar - have a high degree of control over the frequency and modulation of the field. They can sense other animals using electroreception on similar frequencies and shift to avoid jamming each other, and some species use it for active communication.
With these sophisticated uses of electricity, it seems plausible that, in an environment with a lot of different species using active electroreception, prey species and smaller predators sense attackers' electric fields and respond with deimatic behaviors: startling and warning displays. This is similar to the patterning employed by butterflies, variously signaling (or bluffing) about their poisons or trying to mimic different predatory animals. Because these displays are about adding to a creature's electric field rather than removing it, they can use the same type of electrogenerating organs as other existing behaviors such as communication.
