They are green, purple, and brown fish (respectively) in blue police uniforms and hats. The green and purple fish have black mustaches, while the brown fish wears a brown mustache. The purple fish is the biggest, with the brown fish being the smallest.
Role in episode
They appear when they are gathered to inspect suspects for "unspeakable crimes." Instead of finding the key like SpongeBob had hoped, the green cop finds Neptune's Jewel of the Sea in the baby's diaper. The purple cop shakes all of the Butler's personal belongings out of him to find out that he is actually Orin J. Ruffy, a criminal who stole over $75,000 worth of ham sandwiches.