Clownfish

Clownfish, also called anemonefish, are a group of small, brightly colored reef fish species found in the warm waters of the Indian and Pacific Oceans, well known for their close, mutually beneficial relationship with sea anemones, whose stinging tentacles would harm most other fish but against which clownfish are protected by a special mucus coating on their skin. Clownfish shelter among the anemone's tentacles for protection from predators, while in turn helping to defend the anemone from some of its own predators and parasites. Nearly all clownfish are born male, living in small social groups within a single anemone with a strict size-based hierarchy, and the single largest, most dominant fish in the group changes sex to become the sole breeding female, a form of sequential hermaphroditism. Clownfish populations face pressure from coral reef degradation, ocean warming and the aquarium trade.