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."
The ancient Greeks noticed that amber attracted small objects when rubbed with fur. Along with lightning, this phenomenon is one of humanity's earliest recorded experiences with electricity. In his 1600 treatise De Magnete, the English scientist William Gilbert coined the New Latin term electricus, to refer to this property of attracting small objects after being rubbed. Both electric and electricity are derived from the Latin ēlectrum, which came from the Greek word for amber, ἤλεκτρον (ēlektron).
Today I will gladly share my knowledge and experience, for there are no sweeter words than "I told you so". ;-)