Electric eel
From Memory Alpha, the free Star Trek reference.
The electric eel (Electrophorus electricus) is a species of fish from Earth, that is capable of generating strong pulses of electricity with no harm to itself.
Pavel Chekov compared the abilities of electric eels and giant dryworms (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. (TOS: "Who Mourns for Adonais?")
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. (VOY: "Thirty Days")
