Electric organs are modified muscle tissue that can generate electric current. They are usually found on the sides of the body (electric catfish) or on the tail (sea fox). They consist of many muscle plates separated by jelly-like connective tissue. Each plate is approached from below by a nerve ending. The upper part of the plate is positively charged, while the lower part is negatively charged. Electrical discharges occur under the influence of impulses from the spinal cord. An exception are the electric organs of the electric catfish, which are derived from skin glands. Specialised electric organs in the stingray, electric eel and electric catfish generate a voltage of up to 900 V and are used for hunting and defence.

They vary greatly in location, shape and internal structure in different fish species. They can be kidney-shaped (in stingrays and electric eels), a thin layer under the skin (electric catfish), filamentous (mormyrus and gymnote) or located in the suborbital space (North American starfish). Their mass can reach 1/6 (in electric rays) or even 1/4 (in electric eels and catfish) of the body weight.

Each electric organ consists of numerous electric plates arranged in columns - modified (flattened) muscle, nerve or gland cells, between the membranes of which a potential difference can be generated. The number of plates and columns in the electric organs of different fish species varies: in the electric stingray there are about 600 arranged in the form of honeycomb columns of 400 plates each, in the electric eel there are 70 horizontally arranged columns of 6000 plates each, in the electric catfish the electric plates (about 2 million) are randomly distributed. The plates in each column are connected in series and the electric columns are connected in parallel. The electric organs are innervated by branches of the vagus, facial and lingual nerves, which approach the electronegative side of the electric plates.

The electrical discharges generated are used for defence, attack, intraspecific signalling, orientation and finding prey in murky water. The electroreceptors that detect changes in the electric field are thought to be located on the head connective tissue, the lorenzium capsules, which open with a thin channel on the surface of the skin, and the receptors of the lateral line channel. Fish with these organs can tolerate without harm voltages that are lethal to other fish.

Electrical discharges from large fish are dangerous to humans.