Peculiar tissues which are emitting electric pulses into the ambient water, derived (in all African and most South American electric fishes) from muscular tissue. In mature Mormyridae situated in the caudal peduncle, in juvenile Mormyridae in the posterior portion of the trunk, to a certain degree comparable to the situation in Gymnarchus. In that fish there are four strings of electrocytes of different length on either side of the trunk which extend to the tip of the long, tapering tail, which lacks a caudal fin. See also electric cell .