The answer is mutualism.
Mutualism is a relationship between two different species in which both species benefit. In clownfish - sea anemone relationship, the clownfish is protected from predators by the sea anemone, so the clownfish benefits from this relationship. The sea anemone gets more prey thanks to a coloration of the clownfish, so the sea anemone also benefits from this relationship. Since both species benefit, their relationship is an example of mutualism.