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.

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.

Mary Bates is a freelance science writer living in Boston. She has a PhD in psychology from Brown University where she studied bat echolocation. You can visit her website at www.marybateswriter.com and follow her on Twitter at @mebwriter.
  • Cynthia

    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:)!

  • kmi

    i never knew pufferfish are talented architects! impressive!

    • I agree – an impressive little fish, indeed!

  • Brent

    That’s one artistic fish!

  • lemanz

    so…. those fishes are aliens!!!

  • Prashanth

    wow thats a great engineer of nature….

  • mokdad

    attracting a female is not an easy job

  • Yatin

    Can we say Its alien fishes?

  • nanai

    I cant get over how artistic a pufferfish is

  • Chudamani akavaram

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

  • Dwayne L.

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

  • lily

    Wow, incredible architect!


    It so amazing


    I wish i could watch that in real

  • arthur

    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?

  • James

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

  • Chaiyapruk Chansap

    Great, engineering and architecture fish

  • Edy Susilo

    Awesome, love that makes it all..

  • Edy Susilo

    awesome, love that makes it all.. 🙂

  • Ryan

    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!

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

  • qwaq

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

  • Jim

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

  • Louise Gabriel

    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.

  • Jay

    Marvelously created fish,,

  • Moonwaterz

    CYMATICS – KYMATICA (man made!)

  • Igbinosa Osaigbovo

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

  • satendra singh

    it’s awesome

  • Jad

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

  • Marielle T.

    Awww! That’s so cool!

  • Fisayo Adesina

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

  • sue fleming

    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!

  • Aditya

    Fantastic !!!

  • Abhishek

    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 ?

  • Ângela Teles

    That’s amazing! What an artistic fish!

    • Thanks for taking the time to comment – I agree!

  • andziwa

    if all male species were like this……

  • jerry lundquist

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

  • Rumby Dust

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

  • Nancy Crawford

    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:) !

  • sachin Das

    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.

  • Mae

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

  • behzad parnian

    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.

  • Galih Abdul Fatah M

    amazing fish

  • Gautam

    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! 🙂

  • Umer

    God gifted creatures …

  • Thalia

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

  • valeed

    Fantastic !!!!!!!!!

  • Lucien Alexandre Marion

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

  • Gomoco

    wow, get some cuties there my man 🙂

  • frank

    It’s the Stargate!

  • Issa

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

  • Picandz

    Wow..its awesome!!!!

    That’s what makes the NatGeo famous for..

  • Sura

    Amazing and likes fotos

  • Vilma

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

  • Alex

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

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

  • briana


  • Paru

    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.

  • navneet shrivastava

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

  • farmer jim

    Wow! Bower Birds of the deep!

  • jose

    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. 🙂

  • Bella Canetaco

    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

  • Ilya

    Here is a video:

  • Bobb

    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.

  • ethan

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

  • Nishi Jain

    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.

  • Lars Stokholm

    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.

  • Troy Daniel

    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.

  • Agnieszka Piotrowska

    I couldn’t believe it when I saw the footage, but we have the same puffer on Ios island in Greece.
    They don’t build circles (at least we didn’t spot any), but they look exactly the same! If it’s a new species, why it’s showing up on the other side of the world in Greece.
    I work in a dive center and have photos and videos to prove.

  • Amit

    Hi! Im intrested to know if the construction which the pufferfish does, attracts other females from another species, and what are the consequences.
    Really appreciate an answer

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