Mr. Policeman Fishy, a fish wearing a police officer's cap, appears during Elmo's imaginary trip underwater, which first appeared as part of a 1989 episode of Sesame Street. While acting as Captain Elmo Cousteau, Elmo finds himself lost under the sea while looking for the missing treasure of the lost soap. He crosses paths with Mr. Policeman Fishy and asks for his assistance. The policefish leads Elmo to the treasure chest containing the missing soap. Then, he lets Elmo hold onto his tail and gives him a lift back up to the surface.
Mr. Policeman Fishy doesn't talk, except in fish language (in other words, he speaks in "blubs"). But being an underwater explorer, Captain Elmo has no trouble understanding him anyway.