Classical conditioning of electric organ discharge rate in mormyrids.

Weakly electric fish of the African family Mormyridae emit pulses at variable intervals with a distribution skewed toward longer intervals. Fourteen specimens of the genera Mormyrops, Gnathonemus, and Marcusenius were classically conditioned to increase briefly their discharge frequency. The unconditioned stimulus was electric shock and the conditioned stimulus was light. These results are novel in that the overt conditioned response involves neither secretion nor movement.