The so-called electric eel is one kind of fish that produces electrical discharges. They can emit very strong electrical charges, hundreds of volts stronger than a car battery! They use their electricity to shock and kill prey or deter predators. But there are hundreds of other fish species that produce relatively weak electrical discharges– much too weak to hurt or shock you or another fish.
Weakly electric fish use their electric organ discharges for two important functions–communication and navigation. Since many electric fish are nocturnal or live in murky water, they have evolved the ability to "see" their surroundings using electricity.
The electrical field they create reacts differently to different kinds of objects. For example, a rock, a fish, and a plant each conduct electricity differently. The fish detect these differences using electric receptors in their skin, and can therefore move easily around obstacles and find food without using their eyes.
The dark or murky water also makes it hard to find and communicate with others. But electric fish use their electrical discharges to send signals to one another. By varying the frequency or pattern of their electric organ discharges, these fish can create complex communication signals. Behavioral studies of electric communication in these fish have found that electric fish signal this way during courtship, territorial disputes, and other social situations.