Clownfish are All Born Male, a Dominant Male Will Turn Female When the Current Female of the Group Dies

Daven Hiskey 8
Today I found out clownfish are all born males and the dominant male of a group will turn female when the female of that group dies.

Clownfish, also known as anenomefish, are sequential hermaphrodites and live in very regimented schools made up of all males and one female.  The group is made up of a hierarchy with the female fish being the dominant and generally the largest fish in a given group.  The second in command of the group is usually the largest male, who is also generally the most aggressive male of the group.  This male will pair off with the female to breed.  The rest of the males in the area will not breed with the female.

Upon breeding, the female will lay sometimes thousands of eggs close to their home, usually on a rock or coral.  The two will then take turns guarding the eggs until they hatch around a week later.

If the female dies, the dominate male will then begin to gain weight and will become the female of the group.  It will then choose a breeding partner among the available males, which is usually the largest male available.  The two will pair off and breed together until something happens to one or the other, at which point the cycle begins again.

It is thought that this peculiar ability to change sex developed because, unlike many other types of fish, clownfish almost never stray very far away from their homes in sea anemones, which they form a symbiotic relationship with.  Because they stay in more or less one spot their whole lives, it would be very hard for them to find breeding partners if they weren’t able to change their gender.

If you liked this article and the Bonus Facts below, you might also like:

Bonus Facts:

  • Other sea life that are known to change their gender include wrasses, which is a type of fish, and moray eels.  Unlike clownfish, wrasses switch from female to male with the largest female switching to male and taking over a group of females.
  • As mentioned, clownfish form a symbiotic relationship with the sea anemone they live in.  The clownfish eat various small invertebrates and algae that could harm the anemone.  Their feces also serves to help fertilize the anemone.  The sea anemone offers a great deal of protection for the clownfish from predators.  The clownfish also gets food in the way of scraps from the anemone’s food. The clownfish return the favor by using their bright coloring to lure fish into the anemone, which are then killed by the anemone’s poison and eaten, with the scraps going to the clownfish.  Finally, it is thought that the clownfish’s frequent activity in and around the anemone provides better water circulation, which helps the health of the anemone.
  • It isn’t exactly known how the clownfish survive the anemone’s very potent poison.  It is thought that the mucus coating their skin must be made up of some sort of sugar compound, rather than of proteins, which perhaps makes it so the anemone doesn’t recognize the clownfish as a potential food source and so doesn’t sting them.  Clownfish are also somewhat resistant to the toxins in the anemone, but not wholly.  When directly exposed to the toxins, when it penetrates their mucus layer, they will die like any other fish.
  • Clownfish live in warmer water regions in the Indian and Pacific oceans.  They can particularly be found in the Great Barrier Reef and in the Red Sea.
  • Because clownfish breed so easily in captivity and exhibit near constant, quirky activity while awake, they have become extremely popular aquarium fish.
  • Occasionally, humans can also change sex naturally, at least in terms of changing external body parts.  In the vast majority of these cases where the change occurs naturally, a human born with female genitalia, will turn male after puberty.  This is usually due to a 5-alpha-reductase deficiency (5alpha-RD-2) or 17-beta-hydroxysteroid dehydrogenase deficiency (17beta-HSD-3).  Even more rarely, a person born with male parts will naturally turn female after puberty.  How this occurs from a genetic standpoint isn’t currently well understood.  It can also occasionally happen that a male or female human can be born with the opposite body parts and general physical appearance than their chromosome pairs indicate.

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8 Comments »

  1. Andrea September 1, 2011 at 4:36 pm - Reply

    “Occasionally, humans can also change sex naturally, at least in terms of changing external body parts”

    Oh wow. This is insane! The whole time I was reading this article I was thinking about what would happen if humans did this. Weird.

    • Jamie June 8, 2013 at 2:57 pm - Reply

      These guys don’t even surgery…

      Also, I guess that’s what they left out of Finding Nemo…Nemo’s dad Marlin should have become his new mother after his birth mom Coral died. Then she would have picked Nemo as her mate! That is just messed up. Pixar might make good movies, but they are not a substitute for Life Science class.

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