An electric fish is any fish that can generate electric fields. A fish that can generate electric fields is called electrogenic while a fish that has the ability to detect electric fields is called electroreceptive. Most electrogenic fish are also electroreceptive. The only group of electrogenic fish who are not electroreceptive come from the family Uranoscopidae. Electric fish species can be found both in the ocean and in freshwater rivers of South America (Gymnotiformes) and Africa (Mormyridae). Many fish such as sharks, rays and catfishes can detect electric fields and are thus electroreceptive, but they are not classified as electric fish because they cannot generate electricity. Most common bony fish (teleosts), including most fish kept in aquaria or caught for food, are neither electrogenic nor electroreceptive.

Electric fish produce their electrical fields from a specialized structure called an electric organ. This is made up of modified muscle or nerve cells, which became specialized for producing bioelectric fields stronger than those that normal nerves or muscles produce. Typically this organ is located in the tail of the electric fish. The electrical output of the organ is called the electric organ discharge.