Coral reefs are ancient and extremely complex communities functioning as a single unit. Their inhabitants play the unique role and are bound by intricate and obscure interrelations. Reefs are widely spread in tropical zone of Pacific and Indian oceans, where is a lot of sunlight and water remains warm all year round (its average temperature is 26 oC ).
Many reef's inhabitants have bizarre motley colour which helps them to become imperceptible among brightly coloured corals.

The basis of the reef is formed by calcareous skeletons of madreporarian corals. Another type of corals are soft corals (ALCYONARIA), the colonies of small polyps with soft organic skeletons.

The bright clown fishes (Amphiprion sp.) (POMACENTTIDAE) are widely spread in the Pacific and Indian oceans. They live in symbiosis with anemones. Clown-fishes are covered with the special exreted mucous preventing them from stinging by anemone. When the mucous cover is destroyed, stinging cells of anemone may paralyse the fish, then it would be eaten. In the wild clown fishes are never found without anemone. In danger these fishes usually hide among anemone tentacles. There they spawn and, probably, clear themselves from parasites by anemone's stringing cells. In aquarium one may observe how these fishes bring to anemone pieces of food.

Triggerfishes (BALISTIDAE) are usually very brightly coloured and are the typical inhabitants of coral reefs. The first spine of their dorsal fin is very powerful and can be fixed in a vertical position with the help of the second one. In danger a triggerfish hides in a narrow shelter and lifts its dorsal and abdominal spines so that it is impossible to pull it out.
Strong teeth of triggerfishes help them to bite off parts of corals, crush shells of molluscs, sea urchins and crabs.

The bright butterfly fishes (Chaetodon sp) (CHAETODONTIDAE) swim through the corals. Their diet consists of coral polyps and it is very difficult to keep them in captivity. A few species are obligatory omnivorous; others prey on small invertebrates.