Electric sense (i.e., the ability to detect low-voltage electrical impulses from other individuals) is found in most primitive fish orders, a few derived teleost fish, some aquatic amphibians, the platypus, and the echina. Electric signals (i.e., self-generated electrical signals used for communication) are best understood in the weakly electric fish. Weakly electric fish include three freshwater teleost groups that produce dual-purpose electric signals to locate objects and communicate in the dark. Their electric organ discharges (EODs) are distinctive to species, and often to age, sex, and condition. EODs are nonpropagating electrostatic fields, detectable only a few body lengths from the signaler. Electroreceptive predators may eavesdrop, and many weakly electric fish have signal adaptations that make their signals cryptic to predators. EODs are triggered by nerve impulses, but their waveform shapes are regulated by steroid and peptide hormones. The electric eel is a specialized electric fish that produces a low-voltage EOD for electrolocation and communication and also a high-voltage discharge to stun prey and defend itself.
