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Clownfish Facts You Won’t Find in Disney Cartoons.

Updated on June 9, 2013

Some basic clown fish facts

The common name clown fish is used to describe a group of brightly colored fish in the damselfish family. The facts that have made them quite remarkable include their mysterious ability to co-exist in a close relationship with deadly anemones and to change sex! All clownfish start off as males and the most powerful fish gets the privilege of changing to a fertile female. They didn’t tell us that in Finding Nemo!

The common clown fish
The common clown fish | Source

Setting up a clown fish home next to a lethal anemone

In the wild clown fish are found in shallow lagoons in close association with coral reefs in the warm waters of the Pacific and Indian Oceans. Their natural habitat stretches to northwest Australia and Japan. They have developed a remarkable symbiotic relationship with sea anemones from which both organisms benefit. The advantages to the clown fish are obvious, the anemone gives them incredible protection from their predators. They also benefit by getting the undigested scraps from the food of their host anemone. In return the small fish help the anemone by eating parasites that might harm it, eating its dead tentacles and cleaning it of algae.

There is also a suggestion that the swimming of the fish around the anemone increases airflow over it, which is beneficial. Some people reckon that the clown fish attracts victims to the anemone, by swimming out, attracting bigger fish with its bright colors, which will then chase it to the anemone, where they quickly change from predator to prey, as the anemone stings them and eats them. However, it is hard to be certain whether this represents a serious part of the symbiotic relationship.

Immunity to anemone sting?

What is not completely understood is how the clown fish can swim among the anemone tentacles which have nematocysts, similar to jellyfish, and whose sting is lethal to other fish. One theory is that the mucus covering the scales is rich in sugar compounds, unlike that of other marine fish which is mostly protein, the carbohydrates in the mucus are not recognized as ‘animal’ by the anemone and the clown fish is not stung. However there are also suggestions it must acclimate itself to the anemone, by gradually increasing its exposure to the sting, by rubbing itself against the tentacles, until it acquires immunity. The fact that the fish are very specific the anemones they pick as hosts, only associating with a few species, suggests that they are able to develop immunity against the toxins of specific species of anemone.

Clown fish A. ocellaris in Heteractis_magnifica anemone.  The facts of how it is immune to the anemone's stings are not fully understood.
Clown fish A. ocellaris in Heteractis_magnifica anemone. The facts of how it is immune to the anemone's stings are not fully understood. | Source

clown fish reproduction facts: they all start out as boys!

The reproductive biology of clown fish might strike you as a little bit odd at first glance. The little fish are what is technical known as protandrous hermaphrodites. They are born with both male and female reproductive organs and they all start off as immature male, but have the ability to become fertile females. In the wild they usually live in small hierarchical groups, in which the biggest fish is a fertile female, the next powerful fish is a fertile males, and the other smaller fish are infertile, immature fish. If the female dies, the breeder male changes to a female and one of the infertile males is elevated to breeder status. They didn’t tell you about that in Finding Nemo!

After the eggs are laid and stuck to the ground near the base of the anemone they are looked after by the male, who fans them with his fins, to create a water flow over the eggs which keeps them well aerated, and removes any that are unfertilized or become infected with fungus. Once the eggs hatch and the larvae use up their yolk sack and grow a little bit, they swim away in search of a host anemone home of their own.

Anemone fish in the marine home aquarium

Clown fish are frequently kept in marine aquaria and are the first ornamental fish to be bred in large fish farms on a commercial scale. They are usually kept in pairs and their peculiar reproductive biology means that their keepers do not have to worry about obtaining a male and a female, they just purchase two fish and know that they will end up with a pair, leaving it to their pets to decide which will be the wife and which the husband in the relationship. It is advisable to get two fish that differ in size so they can decide quickly (the bigger one will end up female), so the decision does not involve too many contests in which the fish could hurt each other. In captivity clown fish can be kept without an anemone, which is quite challenging to keep alive in a marine aquarium, although anecdotal evidence suggests that they are happier with a host.


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    • profile image


      7 years ago


    • aa lite profile imageAUTHOR

      aa lite 

      7 years ago from London

      I am not surprised your younger son likes clownfish, they look great and they are supposed to be relatively easy to keep. All this is making me think I should start a marine aquarium.....perhaps when the hubs start paying more.

      Thanks for stopping by

    • Sparkle Chi profile image


      7 years ago from Chandler, AZ

      Wow! How interesting! Clown fish are one of my youngest son's favorites!

    • aa lite profile imageAUTHOR

      aa lite 

      7 years ago from London

      Thanks for visiting, I never had a marine tank, but I used to keep a lot of freshwater cichlids (from lake malawi). Fish were great but I've now moved to frogs and geckos.

    • profile image


      7 years ago

      Had a Salt water tank for years. Loved my Clown fish and anemones. I could just sit and watch my tank for hours. Miss it. Good Hub. Noted up :)

    • Shesabutterfly profile image

      Cholee Clay 

      7 years ago from Wisconsin

      I've always found clown fish interesting, you have provided some really great facts about them. I didn't know they chose their sex in that manner. Great hub!


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