The electric eel - Electrophorus electricus

The eel generates electric charge in a battery of biological electrochemical cells, each cell providing about 0.15 V and an overall potential difference of ~ 700 V. Note that the eel's head is the cathode(+) and its tail the anode(-). The cells extend over the length of the eel.
Thanks to Professor Don Stevens, Zoology, for the picture and expert advice.