Clownfish Marine Biology

ORDER: Pomacentridae meaning Damselfishes

Clownfish have a symbiotic relationship (win-win) with anemonesAnemone fish (commonly known as Clownfish) are a sub family of Damselfish – Pomacentridae (image 2).

Damsel & ClownfishThey share a symbiotic relationship with host Sea Anemones (image 1) where both creatures benefit from each other’s presence. One Anemone can host many fish.

Resembling plants, Sea Anemones are infact meat eating animals with stinging tentacles. For more information on Sea and Tube Anemones please visit our Anemone page.

Anemone fish build immunity to these nematocysts by developing a mucus coating on the body. They swim in a unique way differentiating themselves from the prey of the Anemone, this swimming style signals the host not to fire its poisonous sting.

Clownfish, a.k.a. Nemo, in their natural habitat of anemonesIn return for shelter, they are good housekeepers, ridding their host of unwanted parasites and leftover food bits, they are ferocious in defending their territory offering protection from Anemone eating fish such as butterfly fishes.

Clownfish have a mucus layer to protect against the sting of the anemoneShould an Anemone fish relocate it might take days for their coating to develop the correct balance sufficient to avoid being stung. Clownfish and some Damsels are the only fish able to avoid the potent sting of the sea Anemone, but not all Anemones are suitable hosts some will sting and consume potential housemates.

Many species of Anemone fish can be observed inhabiting only certain species of anemone, for example as illustrated in Image 3 and 4, the Western Clown Anemone is generally seen living with the H. Magnifica. Others species of Anemone will host many different species of Clownfish.

Clowfish hierarchy: biggest female, 2nd breeding male, 3rd non breeding maleClownfish have a fascinating system of hierarchy within their community, which prevents conflict within the group. The largest fish is always the female, the second largest is the breeding male, the rest are all males, juveniles usually look different to adults and they are all hermaphrodites.

Residue of the Anemones compound visible on the fish's mouthWhen the female of the group dies the dominant male will change to a female and take her place, this change is irreversible.

All other fish in the group will move up one place, the next male in line then becoming the dominant male and interestingly each fish is exactly 20% smaller than the one above it.

Males tend the eggs, fanning them to keep them oxygenatedWhen environmental conditions are suitable the female will lay her eggs on a flat surface close to or beneath the host Anemone, if none is available she will move something close by. The male externally fertilizes the eggs.

The anemone releases a compound, which the adult fish gently blow onto the eggs and its thought that this aids in building up the juveniles immune system.

Clownfish Eggs amongst sea anemonesIt is generally the male who guards and tend the eggs, fanning them to keep them oxygenated, this fascinating behavior is shown in Image 7 & 8, we can even see the residue of the Anemones compound on the fish’s mouth in image 7.

The moons cycle dictates when the eggs hatch. The pelagic larvae float in the water column until the time of metamorphosis when they become juveniles.

Juvenile Clownfish always look slightly differentIts very difficult for these youngsters to find a host and unless they find an anemone without an existing community or find a group with a vacancy due to a death they could well be left homeless and vulnerable to predation.

Many do end up as fish food.

Fortunately the juvenile illustrated in image 10 has found an available anemone although he must swim carefully until his mucus covering has developed sufficiently enough to avoid its stinging nematocysts.

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