Lure fish

Lure fish are a kind of non-carnivorous fish that lived in the River Thames, at least during the frost fairs. They had green lights on their heads. They were attracted by sound.

They swam around under the ice and lured people away from the crowds to suck people under the ice to be fed to a sea serpent chained below.

A stallman would go fishing during the nights to catch these fish, and proceed to use them in pies in his stall that he could sell. (TV: Thin Ice)

Behind the scenes

 * The fish resemble anglerfish due to the light sticking out from their heads and their tendency to lure people towards it. However, anglerfish are carnivores, and according to the Twelfth Doctor, these fish are not.