Anemone fish are some of the most charismatic and famous fish on the reef. There are twenty eight species, the most famous being the true clownfish, now often known as ‘Nemo’.
Nemo, like all anemone fish, live in anemone hosts in a mutually symbiotic relationship. This means both parties benefit by the relationship; the fish get a safe home and food scraps and the anemone gets increased circulation from the fish movements, and nutrition from the fish faecal matter. Clownfish will generally be host specific to particular anemone species and can home in on them using chemical receptors.
Anemone fish are part of the damsel fish family, which also include the pretty blue green chromis and territorial algal grazing staghorn damsels. They live for 7-9 years and will generally stay in the same anemone home for the majority of their lives. They are omnivores; feeding on both small invertebrates and algae.
Anemones are part of the phylum Cnidaria which also encompass jellyfish and corals. They have stinging cells or nematocysts which are used to paralyse their prey. There are a couple of anemone species that are even lethal to humans! However, clownfish are not stung by their anemone hosts; scientists think they could have become ‘immune’ to the stings over time. It is also thought they have protective mucus over their scales. This mucus means the anemone does not recognise the clownfish as potential prey.
All baby clownfish hatch as immature males, and there is only one female and one dominant male in each anemone. If the dominant female dies the next male down on the ‘pecking order’ will undergo sequential hermaphroditism and become a female! The female lays eggs outside of, but close to the anemone around the full moon. It is then the dominant males’ job to look after the eggs during their development. He does this meticulously, blowing water over the eggs frequently to ensure there is enough oxygen and to rid them of parasites. Generally about 8 days later the babies will hatch and dependant on the species will either return to their natal anemone or find a new one, though generally on the same reef.
In the wild, all clownfish species will live among the tentacles of an anemone. The clownfish manages to avoid being injured by the dangerous anemone because it is coated with a protective slime. The clownfish has a symbiotic, or mutually beneficial, relationship with the sea anemone. It catches most of its food by co-operating with its host anemone. The clownfish will leave the safety of the anemone’s tentacles and swim out among the nearby reef. Its brilliant colors attract larger fish, who, lured by the thought of a meal, follow it back to the anemone and are stung by the anemone tentacles. The anemone then consumes the fish, and the clownfish feeds on the remains.
All clownfish start off male. Clownfish live in small groups with a well established hierarchy. The largest male will be at the top of the hierarchy and eventually morph into a female. The second largest male will form a couple with her and they will breed.