Cleaner Wrasse-Predators-
At 'cleaning stations', sharks, eels and other predatorily reef creatures are often present and allow Cleaner Wrasse to clean both outside and inside their body, in order to become free of parasites and disease. This incredible mutual relationship between fish near the top of the food chain and Cleaner Wrasse, demonstrates that because of the useful service provided by the Wrasse, which prolongs and benefits the life of the predator, they are exempt from feeling the wrath of any natural predators.
Above is a Lemon Shark which has resisted eating the Cleaner Wrasse and allowed the Wrasse to clean inside his mouth