Comparative aspects of brain organization of an african "wave" electric fish, Gymnarchus niloticus

Gymnarchus niloticus, one of the less-well-known electroreceptive teleost fishes, is the only African mormyriform fish with a wavelike or tone electric organ discharge. For Gymnarchus, this is the first detailed description of the lateral line lobe, vestibulolateral lobe, cerebellum, and midbrain torus semicircularis-central electrosensory structures. Brain organization in Gymnarchus closely resembles that of mormyrids. In particular, the lateral line lobe is a bilateral structure with three cortical zones-ventral, dorsal, medial-and a fourth central zone of large cells. The convergent evolution of the electric sense of mormyriform and gymnotoid fish, and its central representation, is discussed.