Eel

Eels were a type of fish that lived on Earth. The Eighth Doctor once caught one whilst fishing in Vienna. (PROSE: The Sorrows of Vienna)

Eels were the main ingredient in jellied eels. (TV: Combat)

Sleeks were giant electric eels which were time-sensitive. (AUDIO: The Thief Who Stole Time) On Funderell, the Wavewalkers worshipped a sleek known locally as Funderell's Daughter, or the Great Sleek. It served as their guardian. They consulted it for advice, and sacrificed to their god. Sartia killed the Great Sleek in self-defence with her staser. According to the Fourth Doctor, she committed deicide. (AUDIO: The Skin of the Sleek)

Behind the scenes

 * The Voord were originally scripted as "eel-like". (REF: Doctor Who Monsters: A Bestiary)