Another name for these animals is anemone fish because they live in close association with sea anemones, themselves quite aggressive invertebrates that feed upon small fish, crabs and plankton. The food is caught by the anemone's tentacles which are themselves armed with powerful stinging cells called nematocysts, and coated by a sticky mucus. Biologists were at first confused about how the clownfish could swim unharmed among the stinging tentacles of the anemone.

The answer to this conundrum was solved a number of years ago when it was realised that the clownfish have a clever means of immunising themselves against the stinging anemones. Before adopting an anemone as a safe haven the clownfish carefully rubs itself against the mucus clad tentacles, coating its own body with the anemone's mucus. It seems that the anemones do not then recognise the fish as either potential food or potential enemies and the clownfish are then free to swim among the tentacles unharmed.

A problem arises however with the offspring of clownfish; how to protect them from the potentially lethal adopted guardian? The parent fish deposit their eggs on rock surfaces underneath the anemone and they regularly tend to them by blowing water across them, ensuring a regular supply of oxygen-rich water and preventing fungal growth. In order to protect the actual eggs from the stinging anemone's tentacles the parent clownfish takes a mucus coated tentacle in its own mouth and then rubs it gently over the developing embryos within the attached egg masses prior to them emerging as vulnerable fry. As soon as the baby fish do hatch they can avoid predators by hiding among the protective tentacles of the anemone. There they can grow up in safety until they move off to establish their own new home.