Symbiotic mutualism

Clownfish or Anemonefishes consist of thirty species that all form symbiotic mutualisms with sea anemones. They thrive together, exchanging food and protection to each other.

The main benefit for the clownfish is the protection from the anemone due to its poisonous tentacles. A sea anemone normally captures prey such as small fish swimming through their stinging tentacles, which they then start to digest. The clownfish is resistant against the poisonous tentacles of the sea anemone and therefor the anemone provides a safe nesting area and protection against predators.

Clown fish feed on undigested leftovers of anemone prey, they occasionally eat dead anemone tentacles, and can feed on various algae and plankton located on and near the anemone. The feeding on algae and leftovers serves as a cleaning job at the same time. It’s thought that the bright colors of the clownfish lure small fish into the anemone which gives the anemone an extra meal. The clownfish defends the anemone against predators such as butterflyfish and parasites. The fecal matter of clown fish are also very appreciated by the anemone: the nitrogen contained in the clownfish excrement boosts the algae growth in the tissue of anemones, that in turn contribute to growth and regeneration of the anemone.


Clownfish also increase water circulation through swimming around the anemone to increase oxygen intake of the anemone. Because of this mutualistic relationship, anemones habited by clownfish are overall larger than anemones without them and clownfish are more likely to survive. It’s still not very clear how clownfish can survive the poisonous sting, or be undetected by the stinging mechanism of the anemone. There are 2 theories, based on either camouflaged skin mucus (that consists of sugars rather than protein, the latter being the condition for the stinging trigger), or an adaptation of some clownfish species to their host which allows a form of immunity against the sting.

In Koh Tao the species Black Saddleback Clownfish and the Pink Anemonefish (or Skunk Anemonefish) are found. Some seem a bit shy, but they can have a good sense of curiosity as well.

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