Electric eel

The electric eel (Electrophorus electricus) was a species of fish from Earth that was capable of generating strong pulses of electricity with no harm to itself.

Pavel Chekov compared the abilities of electric eels and giant dry-worms (of Antos IV) to those of Apollo, in explaining his apparent ability to tap a flow of energy from an unknown source and channeling it through his body against the crew of the USS Enterprise (NCC-1701). 

The Delta Flyer encountered a giant creature akin to an electric eel while exploring the depths of the Monean Waters in 2375. The creature emitted massive thermic discharges exceeding 500,000 volts, which disabled the Flyer.