In the hit movie Finding Nemo an overprotective clownfish named Marlin searches for his son Nemo.
The true protectors of clownfish in the ocean, however, are not parents but rather prickly, stinging sea anemones that live on reefs.
Clownfish, also called anemone fish, are small - largest (13cm) and are usally devoured by larger fish such as grouper.
For protection, clownfish seek refuge amongst the tentacles of sea anemones which contain harpoon-like stinging capsules used to capture prey and ward off predators.
Clownfish have mucus on their skin that somehow protects them against the sting of their host anemone. As a result, the clownfish are able to stick near their host which is avoided by most other fish in the sea. If you remove the clownfish, large butterfly fishes will eat the anemone.
Butterfly fish are predators of the sea anemone. Clownfish scare off butterflyfish from the anemone. So, the protection of the anemone is part of the mutual relationship.

In addition to scaring off predators, some scientists speculate that clownfish waste may serve as a nutrient for the anemones.