Eel

Eels are cold-blooded aquatic vertebrates with serpentine bodies and a minimum of appendages. True eels are fish, although throughout the galaxy there are numerous species of animals referred to as eels.

Some eel-like creatures were seen swimming in a lake on Archer IV. 

The Xindi-Reptilian biorifle weapon is powered by a lifeform resembling an eel. Its neural pathways modulate the weapon's power output. 

The Xyrillian ship encountered by the in 2151 had a tank in which eel-like creatures could be seen swimming in liquid through windows.