Cleaner fishes (and some shrimps) set up "cleaning stations" on the reef where larger fish come to have their parasites removed by these specialized predators.  These fish are often brightly colored to "announce" their presence and customers arrive and remain motionless while the cleaner goes about its work.  Sometimes the cleaner actually enters the mouth of the customer and removes the parasites! Amazingly, the customers never seem to eat the cleaners and fish even line up to wait their turn without disturbing the other fish.