My vote goes to "lightning eel" or "thundering eel", as I assume that people were struck by lightning long before they were zapped by eel. Or at least the phenomena was more known.
Wikipedia mentions something about it:
"Long before any knowledge of electricity existed, people were aware of shocks from electric fish. Ancient Egyptian texts dating from 2750 BCE referred to these fish as the "Thunderer of the Nile", and described them as the "protectors" of all other fish."