A Klabnian eel is an eel from Klabnia.
Q threatened to use his powers to turn Vash into a Klabnian eel in 2367. (TNG episode: "QPid")
In 2369, Odo commented that Quark was a slippery as a Klabnian eel when referring to how few convictions Odo had brought against him. (DS9 video game: Harbinger)