What’s a Pufferfish? Explaining Animal Behind Mystery Circles

Mystery circles on the seafloor have intrigued divers for decades, and scientists recently identified the culprit: a new species of pufferfish.

This tiny architect—which builds elaborate nests to woo females—has also captured the hearts of our readers, with more than 60 comments and 30,000 Facebook likes on our story about the phenomenon. So we wondered: What’s a pufferfish?

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

It turns out there are 120 pufferfish species in the Tetraodontidae family. The fish live in warm, coastal waters around the world, and some even live in fresh water.  They tend to have tapered, torpedo-shaped bodies with bulbous heads and large eyes.

Pufferfish have four large teeth that are fused together to form a beak-like structure. While some species of pufferfish use their beaks to scrape algae off rocks and coral, certain large species use their beaks to crack open crustaceans and shellfish.

They also come in a variety of colors and sizes, from the 1-inch-long (2.5-centimeter-long) pygmy puffer to the giant freshwater puffer, which can reach 2 feet (0.6 meter) in length.

Puffer Upper

Pufferfish are best known for their ability to “puff up” into a ball several times their normal size. Scientists think the fish developed this defense to compensate for their slow, clumsy swimming style.

A pufferfish might look like an easy meal to a predator, but if pursued, it will quickly fill its extremely elastic stomach with large amounts of water, making itself much bigger and nearly spherical in shape (below).

guineafowl pufferfish picture
A guineafowl pufferfish swims in Hawaiian waters. Photograph by David Fleetham, Corbis

Most species are also covered with small spines that only stick out when they are inflated. A predator that doesn’t heed the pufferfish’s warning may be in danger of choking to death on the spiky, spherical fish. (Watch a video of pufferfish inflating to escape prey.)

But the pufferfish’s defenses don’t stop there: Many species are highly poisonous. Certain pufferfish contain the neurotoxin tetrodotoxin, mostly concentrated in the fish’s liver, gonads, and skin. Although this potent toxin can kill some predators (including people), others, such as sharks, are able to withstand a pufferfish meal with no ill effects.

Dangerous Delicacy

Despite the risks of ingesting tetrodotoxin, pufferfish are a delicacy in many parts of the world.

In Japan, only trained and licensed chefs may prepare pufferfish, known as fugu. Young chefs spend years learning how to properly prepare fugu, making sure that it is free of the toxic liver, gonads, and skin. Even with these precautions, several people die each year after ingesting improperly prepared fugu dishes. (Watch a video about pufferfish as a delicacy.)

Symptoms of tetrodotoxin poisoning begin with numbness in the tongue and lips, followed by headache, dizziness, and vomiting. In the worst cases, sufferers experience rapid heart rate, decreased blood pressure, muscle paralysis, and respiratory distress. Death can occur within four to six hours. The toxin typically kills by paralyzing diaphragm muscles and causing respiratory failure.

Not all pufferfish are toxic, and some species are easier to prepare safely. To keep U.S. consumers safe, the Food and Drug Administration has teamed up with scientists at the Smithsonian’s National Museum of Natural History to create a library of pufferfish DNA. When a tetrodotoxin poisoning occurs, officials can use the library to identify the species of pufferfish that was consumed and determine whether it was illegally imported.

Zombie Fish

The pufferfish’s tetrodotoxin is so powerful that some believe it even has the power to create real-life zombies.

In the 1980s, ethnobotanist Wade Davis—now a National Geographic Society Explorer in Residence—traveled to Haiti to investigate reports of zombification. During his research, Davis discovered that the voodoo sorcerers believed to be capable of turning people into zombies used homemade powders in their rituals. Davis collected and tested samples of zombie powders and discovered they contained pufferfish tetrodotoxin.

Pufferfish tetrodotoxin works in part by preventing neurons from firing. People who ingest the toxin and don’t die within the first 24 hours typically survive, although they often fall into a coma-like state for several days. (Also see pictures of “nature’s walking dead.”)

Completely paralyzed but fully conscious, the victims are pronounced dead and buried. After a few days, the voodoo sorcerer returns and claims the body, which then seems to rise from the dead.

Tell us: What’s your favorite thing about pufferfish?

Follow Mary Bates on Twitter and Facebook.


  1. mason
    planet mars
    March 14, 10:45 am

    wowwwwwwwwwwww this fish is cool just how its puffs up never before seen by me awesome…

  2. vanessa
    October 17, 2014, 2:31 am

    Why is almost every comment so negative? I thought the article was good, informative, covered multiple interesting sections regarding puffer fish. How do they know circles are to attract females? Lol um because they’re scientists and researched hello? ! ? Great job NG

  3. bobbybob90
    January 8, 2014, 1:51 pm

    i don’t no why that fat fish is fat ?????

  4. CC
    September 8, 2013, 4:32 pm

    i cannot help but compare it to our crop circles … if the male puffer takes 10days to create a nest and the only way it can seen is if she is swimming over it — or flying

  5. Jennifer
    Boise, ID
    September 7, 2013, 2:47 am

    Here is a link to the original scientific report with videos at the bottom of the report. So amazing!

  6. Laith
    UK ,Manchester University
    September 6, 2013, 5:30 am

    Apologize for what guy ..???
    absolutely to the typical drama of lack missing absence data or to mysterious story that NG’s topic has .!!!!
    some more of this tailless stories from NG , No thanks ….

  7. essyvon
    September 5, 2013, 6:55 pm

    To all the negative commentators:
    If you read the introduction, this is obviously a follow-up article about the puffer fish, not the original one about the nests. Read the link in the first paragraph “scientists recently identified the culprit” and apologise!!!

  8. Laith
    September 5, 2013, 2:50 pm

    For god sake where is the details ?
    I do’nt believe that all that perfect architectural forms are a fish mind’s design ,There is a missed point

  9. Carlos Rodrigues
    September 5, 2013, 1:36 pm

    I’m sorry, but to say that this is the work of pufferfish to impress the female of the species does not convince me. Only by seeing them doing this job for me to be convinced …

  10. Tom Orred
    Calif. and New Mexico
    September 5, 2013, 1:21 pm

    I have been diving since the mid 50’s, 25 years professionally. Of all the fish in the oceans, I admire the various types of puffer fish as one of my favorites. I find it fascinating on how they puff up when frightened and then watching their little pectoral fins still move them gracefully around. I hate to see them sold as souveniers, dried and all puffed up. I can’t understand the thrill of eating them for the high either. Would you eat a dart frog or tarantula?

  11. S. N. Rama Raju
    Rajapalayam, India
    September 5, 2013, 11:06 am

    A video of making the circle would have thrown more light about the behaviour of this fish

  12. Sérgio Torres
    September 5, 2013, 9:46 am

    Look’s like Stargate transport rings!!

  13. Sebastian
    September 5, 2013, 9:26 am

    But, what about the circle in the sand,how he made it?
    some picture about that??
    it seem, nothing behing the circle, seriuosly…

  14. Miki
    September 5, 2013, 9:13 am

    Everything seems a “tease” when you don’t know what’s coming. Like the answer to a magic trick! However, “knowing” fills your need. In a way I am rather amazed. My father and I fished in New Jersey for years catching a local “puffer.” It was the only fish I wasn’t allowed to clean. It tasted and looked very much like “Shrimp.” Now, I understand why he did the preparation. Thanks NG for the info.

  15. Defiant
    September 4, 2013, 11:21 am

    LAME. The article certainly failed to deliver. A better title would have been “Puffer-fish Information Dump With One Line of Information About the Topic in the Headline.”

  16. Diane
    pufferfish nest
    September 3, 2013, 10:17 pm

    I’m also disappointed. Nothing mentioned about the circles

  17. sherbien
    September 3, 2013, 5:02 pm

    I love pufferfish meat. There are people in far flung islands who cooks pufferfish here.

  18. Aphouya Golanda
    September 3, 2013, 2:10 pm

    This picture keeps popping up on my FB page on a daily basis. OK. I read it once. Wasn’t impressed with the BIG MYSTERY theme. It’s not a mystery if you know what caused it, which was pretty cool. But as I said, I read the article and moved on. So why is it still showing up? If I block it, will I lose any future postings?

  19. azia
    September 3, 2013, 1:06 pm

    Im disappointed with the article, it does not mention how these mystery circles are formed, it is briefly mentioned in the title OS the article but no in-depth information. A video works have been nice to. Although the info is interesting, I have read on this already so its not news to me. I was hoping to learn about the mystery circle and not the species of pufferfish or voodoo practice :/

  20. Brenda
    United States
    September 3, 2013, 10:02 am

    Where is the information about the nests? If I wanted a biology lesson I’d look up the articles with titles pertaining to that. The article title is purposefully misleading and something I’m seeing more and more of all over the internet. I’d expect better from National Geographic, you are lowering yourself to gossip magazine standards now. People obviously clicked article to read about the nests as was teased.

  21. Adri
    September 3, 2013, 7:45 am

    Podrían enviarlo en español?

  22. Adri
    September 3, 2013, 7:42 am

    Podrían traducirlo al español, por favor?

  23. INGRID
    September 3, 2013, 3:14 am

    why do people want to eat everything that lives on this planet,
    I hope they choke on it

  24. Flora Chung
    Calgary, AB, Canada
    September 3, 2013, 2:58 am

    Interesting article.
    But Ima,
    you paint colors to it. Awesome poet.

  25. Irina
    September 3, 2013, 1:49 am

    Here you can see the proces of it:

  26. shaju
    September 3, 2013, 1:23 am

    The article is on “What’s a Pufferfish? Explaining Animal Behind Mystery Circles” and nowhere did the article describe about the mysterious circles except as a word in a sentence.
    However the article with the rest of the topic is good.

  27. Thaddeus Villasor
    September 3, 2013, 12:06 am

    They swim like Zeppelins gliding gracefully under water. Interesting to study up close.

  28. Scott Kuli
    Windsor Ontario
    September 2, 2013, 10:40 pm

    Nonsense! It’s clearly the work of aliens, just like lenticular clouds are flying saucers in disguise. They remind the alien conspiracy crowd of crop circles, so it’s obviously aliens. Get a clue people geez!

  29. Mickey
    September 2, 2013, 9:05 pm

    @Sharalyn, actually there’s a link to the previous article explaining how it was done (see link at the top). There’s also a YouTube video in the comments of that article.

  30. Duane
    September 2, 2013, 9:02 pm

    Sharalyn, I agree with you. I have been a diver for a good number of years and have seen pufferfish all over. I have never seen this design on the ocean floor. This photo was posted earlier in the year by a not so reputable entity and I was very surprised to see Nat Geo post the same photo with no explanation or video indicating that a pufferfish made it. I am very skeptical and this is certainly not up to Nat Geo standards without some kind of verification.

  31. Chris
    September 2, 2013, 8:15 pm

    There is a deflated pufferfish in the top photo in the center of his nest. They look like a regular fish when not in threat mode. I do not understand the attraction to eating something that may kill you..

  32. Eric
    August 26, 2013, 8:39 pm

    We have made pufferfish soup for many years in Korea. But, as you know it would be dangerous, people who can make a dish using pufferfish should get a license for special training how to manipulate it.
    Though some accidents rarely happens, many people love the pufferfish dishes.

  33. Sharalyn
    Fairfield, IA
    August 26, 2013, 5:46 pm

    This is a remarkable design in the photo. You say the pufferfish made the design but give no reasonable explanation of how it was s created. I know Nat Geo is a respectable place, but this is not something I want to take your word for.You say the pufferfish in the photo did it, but how about giving us a VIDEO of it creating it so we can see it for ourselves? Thanks.

  34. Fathi H.
    Saudi arabia
    August 26, 2013, 3:24 am

    Pufferfish is commonly known as inflated, but I never saw it deflated.

  35. Ima Ryma
    August 22, 2013, 3:28 am

    I am a pufferfish, I am.
    I can puff up like a balloon,
    So some wanna have lunch can’t cram
    Me down its tummy overstrewn.
    But if the predator persists,
    As I inflate, my spikes stick out.
    If ingested, I make some twists.
    The predator’s choked up – no doubt!
    But humans are the sneaky kind,
    Grabbing with hooks and nets and stuff.
    I’m delicacy to eat, they find.
    It matters not how much I puff.

    So humans, catch me if you will,
    And eat me and get deathly ill.