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What’s This Mysterious Circle on the Seafloor?

What creates mysterious circles on the seafloor? No, it’s not aliens of the deep—it’s actually pufferfish hoping to snag a mate, a new study says.

Divers first noticed the 6.5-foot-wide (2-meter-wide) circular structures near Japan‘s Amami-Oshima Island about 20 years ago. But no one knew how these so-called mystery circles were constructed—or what was creating them—until now.

seafloor circle picture
A male pufferfish (center) made this nest to lure females in Japan in 2012.
Photograph courtesy Kimiaki Ito

The circles, scientists say, are actually nests created by male pufferfish, which spend about ten days carefully constructing and decorating the structures to woo females. What’s more, this industrious pufferfish is thought to be a new species in the Torquigener genus, according to the study, published July 1 in the journal Scientific Reports.

Nesting Instinct

The male fish, which measures less than 5 inches (13 centimeters) long, first uses his body to create peaks and valleys in the sandy bottom around a central circle of smooth sand. He accomplishes this feat by swimming in toward the center of the circle in a straight line and then back around the center in a circular motion. (Watch a pufferfish video.)

Before the female fish arrive to inspect his handiwork, the male forms irregular patterns in the fine sand particles of the central circle. He also decorates the peaks of the outer portion with shell and coral fragments.

When a potential female partner arrives on the scene, the male stirs up the fine sand in the nest’s inner circle. If she deems the nest, and the male who built it, satisfactory, she lays her eggs in the center of the nest and leaves.

pufferfish picture
A male pufferfish uses his body to create peaks and valleys in the sand. Photograph courtesy Kimiaki Ito

The scientists aren’t sure exactly what the females are looking for when they judge a male’s nest. It could be the central patterns made of fine sand, the decorations on the outside, or the nest’s size or symmetry. (Also see Help Name This Mystery Fish.”)

But they do know that because the nest-making process is so time-consuming, a larger nest could indicate a stronger or more fit male—both desirable traits to females.

Dad Duties

Once the female splits, though, it’s the male who does the parental chores: He remains in the nest until the eggs hatch six days later.

Afterward, the male looks for a nearby spot to start the nest-making process all over again, which is a mystery of its own: Why spend all that time and energy building a brand-new nest? The scientists think it has something to do with the fine sand particles that make up the smooth center of the circles. (Read “Africa’s Mysterious ‘Fairy Circles’ Explained.”)

The males use up all the fine sand within the radius of their nest during a single spawning cycle. To construct another nest, they have to look elsewhere for a site with more fine sand particles.

Now that’s what you call a labor of love.

Follow Mary Bates on Twitter and Facebook.


  1. Troy Daniel
    June 3, 10:52 pm

    I think it does this to keep the eggs from drifting. It’s a way to fight the currents and keep eggs together long enough to hatch. No creator necessary for that. Just a smart little fish.

  2. trim
    September 19, 2013, 7:40 am

    Fish OCD

  3. Lars Stokholm
    September 6, 2013, 1:32 pm

    Why should evolution “invent” such an elaborate, artistic and energy-consuming way of reproduction? Why not just save the time, and let the males fight about the females, like so many other species does?
    The aesthetics in these photos, is for me proof of a creator.

  4. Nishi Jain
    September 4, 2013, 2:21 am

    Wow, nature really has its ways of natural selection. Who would have thought a tiny fish was capable of something as complicated and mathematical as this. Humans really take too much credit for themselves. Nice choice of topic, Mary.

  5. ethan
    camp rocky
    September 3, 2013, 4:29 pm

    thats amazing i can only wonder what exsist in all the unexplored seas

  6. Bobb
    September 2, 2013, 11:41 pm

    Wow, I hope this little guy found a mate. Would be a drag if he didn’t because of another puffer fish that built a similar nest 10 feet away. Simply amazing.

  7. Ilya
    August 25, 2013, 9:34 am

    Here is a video:

  8. Bella Canetaco
    August 24, 2013, 9:07 am

    Quisiera ver un video de como este singular pez construye su nido, pues la verdad para ser tan pequeño, apenas 13 centímetros suponen que hace su nido de 2 mt de diámetro; mirando el diseño se ve simétrico, podría decirse perfecto. Como sí el pez “midiera” . Aún incrédula pero en verdad muy interesante. Espero fervientemente ver un video alguna vez

  9. jose
    Brooklyn New York
    August 21, 2013, 12:45 pm

    With all respect Ms. Mary Bates. but until you and the scientists show me a video of this cute fishy constructing this nest circle, I will believed you. If he did, besides being venomous he is a great mathematician. 🙂

  10. farmer jim
    louisa, Va. US
    August 21, 2013, 9:27 am

    Wow! Bower Birds of the deep!

  11. navneet shrivastava
    August 21, 2013, 2:11 am

    indeed Puffer is hardworking and creative, yet the very fact its posinious makes it interesting.

  12. Paru
    August 20, 2013, 10:39 pm

    Looks like some mini geo activity underneath the floor and the puffer just chisels off, which in itself is remarkable. Remember the location is Japan.

  13. briana
    August 20, 2013, 7:14 pm


  14. Alex
    August 20, 2013, 5:13 pm

    Puffers are some of the coolest fish out there. Best looking eyes in the animal kingdom.

    • Mary Bates
      August 20, 2013, 10:27 pm

      Thanks for the comment! I sure have more of an appreciation for puffer fish after this story.

  15. Vilma
    August 20, 2013, 4:16 pm

    Asombroso ! El pez globo es
    el que resulta venenoso? Es una criatura muy extraña en la Naturaleza

  16. Sura
    Medan Indonesia
    August 20, 2013, 2:29 pm

    Amazing and likes fotos

  17. Picandz
    August 20, 2013, 2:22 pm

    Wow..its awesome!!!!

    That’s what makes the NatGeo famous for..

  18. Issa
    August 20, 2013, 2:13 pm

    And then a plastic bag landed on his masterpiece and ruined his future … Thanks humans!

  19. frank
    August 20, 2013, 1:42 pm

    It’s the Stargate!

  20. Gomoco
    South Africa
    August 20, 2013, 1:38 pm

    wow, get some cuties there my man 🙂

  21. Lucien Alexandre Marion
    August 20, 2013, 1:19 pm

    Nature,.. astonishing are these creations by those fishes…real ART…

  22. valeed
    August 20, 2013, 12:22 pm

    Fantastic !!!!!!!!!

  23. Thalia
    August 20, 2013, 11:59 am

    Es increíble cómo un organismo tan pequeño puede construir algo tan grande y hermoso en comparación a su tamaño.

  24. Umer
    August 20, 2013, 11:56 am

    God gifted creatures …

  25. Gautam
    August 20, 2013, 10:57 am

    Thought only we humans work on our bodies and make ourselves attractive to attract our partners. These creatures are much ahead of us. Guess, its time to learn from them! 🙂

  26. Galih Abdul Fatah M
    August 20, 2013, 8:55 am

    amazing fish

  27. behzad parnian
    August 20, 2013, 8:50 am

    It’s incredible, marvellous and a master piece. Some times I feel that human being has to sit on the knee in front of nature.

  28. Mae
    August 20, 2013, 8:40 am

    @andziwa and @Jad: I totally agree with you
    Real men don’t fertilize and run

  29. sachin Das
    India(Assam , guwahati)
    August 20, 2013, 8:37 am

    A total 31 entrance made by the pufferfish to his parlour with his unique body features that helped to build it just to impress or attract the female one — interesting & need further study.

  30. Nancy Crawford
    August 20, 2013, 8:31 am

    A nest fit for a Queen! Such a little fish to create such as masterpiece with such precision! Wonders of the world we are just finding out about:) !

  31. Rumby Dust
    Zimbabwe, Africa
    August 20, 2013, 8:22 am

    amazing!!! nw we can start putting the blame on land animals for crop circles..lol

  32. jerry lundquist
    gastonia, nc
    August 20, 2013, 7:43 am

    These were the fish that the ancient aliens brought from space.

  33. andziwa
    August 20, 2013, 7:32 am

    if all male species were like this……

  34. Ângela Teles
    August 20, 2013, 7:10 am

    That’s amazing! What an artistic fish!

    • Mary Bates
      August 20, 2013, 10:23 pm

      Thanks for taking the time to comment – I agree!

  35. Abhishek
    August 20, 2013, 5:26 am

    There are more things in heaven and Earth than can be dreamt of ……………….

    Things ike this should teach us to be humble, imagine if this creature had our biological advantages, what not could it achieve ?

  36. Aditya
    August 20, 2013, 5:11 am

    Fantastic !!!

  37. sue fleming
    August 20, 2013, 5:10 am

    I was looking forward to watching a video of the puffer fish making its nest,,, instead was very disappointed to see a promotion for eating said puffer fish!!! So much about conservation of a species doomed to extinction in the wild, in favour of Japanese restaurant business!

  38. Fisayo Adesina
    August 20, 2013, 5:06 am

    Lesson to man: Love is meant to go with responsibility.

  39. Marielle T.
    August 20, 2013, 5:01 am

    Awww! That’s so cool!

  40. Jad
    August 20, 2013, 4:22 am

    Manlier than your stereotypical manly man! This is how us men should roll!

  41. satendra singh
    agra, india
    August 20, 2013, 4:04 am

    it’s awesome

  42. Igbinosa Osaigbovo
    August 20, 2013, 2:49 am

    It just goes to show how wonderful Jehovah’s creations are.

  43. Moonwaterz
    Roman Empire
    August 20, 2013, 2:24 am

    CYMATICS – KYMATICA (man made!)

  44. Jay
    August 20, 2013, 1:59 am

    Marvelously created fish,,

  45. Louise Gabriel
    Manila, Philippines
    August 20, 2013, 1:56 am

    Our World is so wonderful to be destroyed by Climate Change or even us, people of this world. We should focus on life forms here who’s getting extinct rather than going to find life in a planet wherein doesn’t exist anymore.

  46. Jim
    New York, NY
    August 20, 2013, 1:55 am

    He could probably pick up more women by learning to play the guitar.

  47. qwaq
    August 20, 2013, 1:55 am

    At first I thought that was evidence of farting whale 😀 but then i read article

  48. Ryan
    August 20, 2013, 1:13 am

    This is pretty interesting! Even more so if you consider the fat that, without tools, I don’t believe I could created something on that scale with so much symmetry!

    • Mary Bates
      August 20, 2013, 10:24 pm

      I agree, it’s a pretty impressive feat for a little fish!

  49. Edy Susilo
    August 20, 2013, 12:50 am

    awesome, love that makes it all.. 🙂

  50. Edy Susilo
    August 20, 2013, 12:48 am

    Awesome, love that makes it all..

  51. Chaiyapruk Chansap
    Bangkok, Thailand
    August 20, 2013, 12:36 am

    Great, engineering and architecture fish

  52. James
    United States
    August 20, 2013, 12:27 am

    The surprises of nature and the beauty it produces on a daily basis will never stop. Simply amazing little puffer fish

    • Mary Bates
      August 20, 2013, 10:24 pm

      Agreed! Thanks for the comment.

  53. arthur
    August 20, 2013, 12:26 am

    Evolution? Which is harder, to believe that this fish evolved this incredible ability to court the female of its kind, or to believe in a God that actually commands this fish to create this beautiful structure to attract a mate?

    August 20, 2013, 12:22 am

    I wish i could watch that in real

    August 20, 2013, 12:21 am

    It so amazing

  56. lily
    August 19, 2013, 1:26 am

    Wow, incredible architect!

  57. Dwayne L.
    August 18, 2013, 11:03 pm

    I wonder if they taste like chicken? Ha Ha!!!
    But seriously, that’s definitely an incredible feat of engineering for such a small fish.

  58. Chudamani akavaram
    Atlanta, U.S.A
    August 18, 2013, 9:50 pm

    The aboriginal sense of art and love native to fish that is ancestor to man – fish-man, man-fish or human – fish.

  59. nanai
    Papua New Guinea
    August 17, 2013, 6:43 pm

    I cant get over how artistic a pufferfish is

  60. Yatin
    August 17, 2013, 5:59 am

    Can we say Its alien fishes?

  61. mokdad
    August 17, 2013, 3:52 am

    attracting a female is not an easy job

  62. Prashanth
    August 17, 2013, 2:56 am

    wow thats a great engineer of nature….

  63. lemanz
    August 16, 2013, 2:55 pm

    so…. those fishes are aliens!!!

  64. Brent
    August 16, 2013, 2:11 pm

    That’s one artistic fish!

  65. kmi
    United States
    August 16, 2013, 1:22 pm

    i never knew pufferfish are talented architects! impressive!

    • Mary Bates
      August 20, 2013, 10:25 pm

      I agree – an impressive little fish, indeed!

  66. Cynthia
    August 16, 2013, 8:36 am

    it’s so cute of the little fish to do this mysterious job,and consider ur own effort to grasp this truth,you are also incrediblely cute:)!