The incredible "ear stones" of fish

Joshua Foer is a guest blogger on Boing Boing. Joshua is a freelance science journalist and the co-founder of the Atlas Obscura: A Compendium of the World's Wonders, Curiosities, and Esoterica, with Dylan Thuras.


Graham Burnett wrote a fascinating essay in Cabinet recently about otolithic organs, the pair of sensors in the inner ear that help us stay balanced and maintain inertia. "Grossly speaking," writes Burnett, the otolithic organs consist of "a bunch of tiny pebbles (of the white rock known as calcium carbonate) embedded in a gooey wad that sits atop a carpet of delicate hairs." In humans, those "pebbles" are practically microscopic, but in fish, they can be as large as marbles:

There are several thousand researchers around the world who spend their whole working day looking at fish otoliths. This has nothing to do with their physiological functions, however, and everything to do with their structure and the staggering amount of information they contain. In the first place, each species of fish has a unique otolith shape. Couple this with the fact that they are stone (and therefore comparatively resistant to decomposition), and their utility as a biological marker becomes clear. Interested in the food habits of bottlenose whales? Pump their stomachs and you will end up with relatively few bones but lots of otoliths. Find an otolith expert and he or she will be able to give you a menu...

But the true wonder of these peculiar pearls lies within. Should you have occasion to tonsure a snapper or sea-bass, slicing off the top of its skull just above the eyes, you might take a moment to remove the two largest otoliths (there are, as a rule, six in all, three on each side) from their velvet seats to the right and left of the brain stem. With the heel of a knife you should be able to snap one of them in two, and then, holding it to the light, you will discern a set of concentric bands. These are growth rings--annuli--which, properly counted, will give the age of your fish in years.


  1. I remember the first time I got a bad inner ear infection. Woke up in the middle of the night and the entire room was spinning. I had no idea what was going on, but it scared me pretty badly. I couldn’t stand up at all.

  2. Pity you have to kill the animals to get this data. Makes it a rather destructive hobby. If, say, it were kittens this hobby revolved around, people would have a conniption.

  3. I wonder… what energies are required…could dolphins be using lithotripsy to hunt? I mean specifically. Which also makes me wonder if one day GMO cetaceans could do your kidney stones.

  4. “Bottlenose dolphins have the ability to create booms exceeding 230 decibels, mainly as a hunting weapon to stun fish.” anyone examine the otoliths of the prey? Or fragments thereof?

  5. Santa’s Knee here.

    @#4 Talia,

    As one who only hunts kittens as a food source, I have no problem with the ethics of this article.

    As long as one eats one’s kill, do as you wish for science.

    PETA tried to fool me with that whole “Sea Kitten” stuff, but it was just whargarble – nothing can compare to the taste of fresh kittens straight from the dragnet (I support hobo-safe netting practices, btw).


  6. Does this mean that tossing them across a market is cruel, or is that now just throwing rocks?…

  7. @#4

    “Should you have occasion to tonsure a snapper or sea-bass”

    This would most likely be after you CAUGHT the fish to EAT the fish. I imagine that’s why the author chose two edible and very tasty species.

    Some of us eat fish, but few of us eat the heads. Why not do a little investigating?

  8. My girlfriend sometimes has horrible dizzy fits- she says it feels like the room has suddenly flipped upside down. She had a horse-riding accident in her late teens that, in addition to killing her sense of smell for more than a year, knocked a (some?) small piece(s?) of her “ear stones” free of the matrix in which they are normally embedded. Every now and then, one of dislodged stones ‘bumps’ the sensitive hair cells (the “carpet of delicate hairs” Joshua Foer mentions above), and it makes her feel like her world has suddenly lurched upside-down. It’s horribly unpleasant.

    The treatment involves having a specialist suddenly accelerate your head forward while carefully cradling your head and neck in their arms. It looks bizarre, it’s definitely lo-tech, but it works. Apparently the acceleration moves the dislodged stones away from the hair cells.

  9. Also- I work with fish, and I have looked at thousands of these things. They’re beautiful, and as unique as snowflakes, but unlike many of my colleagues, I wouldn’t want to count their growth rings for a living. I have found that by the time you’ve counted your hundredth set of growth rings (and don’t forget you need to do replicates of each count for quality control), the novelty has faded.

    Still, they are beautiful, and they make interesting jewelery:

  10. Mr. Knee: I agree. Nothing beats a fresh grilled kitten fillet on a bun, with ketchup. And a side of fried mice.

  11. Friend of mine does this for a living, a marine biologist doing her dissertation on otoliths in rockfish. She’s hot too.

  12. I used to study otolith formations as a grad student.

    The rings are formed by alternating deposits of protein and calcium carbonate. In tropical fish it is harder to see yearly rings as those usually correspond to seasonal temperature changes. However, it’s possible to see rings corresponding to lunar cycles and even night/day cycles in certain fish.

    Some researchers use zebrafish to study otoliths particularly because they are clear during early development. This allows the researcher to study while the fish grows. However, I won’t lie, most of these fish are also killed during or at the end of the experiments.

    This procedure is called canalith repositioning. Basically, otoconia (mammal’s version of the otolith) are used only for linear acceleration (up, down, forward, reverse, gravity) and when they get displaced they can come into contact with the hair cells responsible for angular acceleration (tilting side to side or turning our heads). Canalith repositioning moves these errant otoconia away from the hair cells they’re disturbing. Vertigo is pretty unpleasant. I’m sorry she has to suffer through it so often.

  13. Ah, memories. I spent a few months on a Polish factory ship cutting the otoliths out of fish skulls by the hundreds. That and playing chess and drinking vodka.

    Good times, good times. Except for the fish of course.

  14. oooooh! I wanna make a canalith repositioning unit. It will involve large rocket motors, lots of room and bacon.

  15. Moriarty,

    230 decibels? That can’t possibly be right.

    Don’t forget, this is under water, much higher SPL possible than in air.

  16. instead of growing their own otoliths, crayfish absorb sand particles into their statocycts. there’s an oft-tried experiment whereupon the biologist replaces the sand in the crayfish’s tank with iron filings, which are then absorbed as otoliths…

    “during the first 24 h the motor activity of the animals increased and was accompanied by frequent strong beats of antennulae on water; animals tried to go away from the magnet attached to the aquarium wall and to hide in a shelter; by the day 10—12, there appeared signs of adaptation to the action of magnet; the animals spent most time near the wall with the magnet and were clinging close to it. If the magnet was moved the animals not only slipped to their side but also rotated around their longitudinal axis. The eyestalks also started moving.”

  17. Do fresh water fish have otoliths as well? I sometimes find rather large remains of Muskellunge and Northern Pike washed up on the shore by my home and it would make for a fun teaching opportunity with my grandson.

  18. @#13 Moriarity – Snapping (and presumably mantis) shrimp can also generate acoustic pressures in excess of 200 db.

    Haven’t been able to determine what one finds in the ears of such shrimp — presumably not much.

  19. Takuan

    Thanks for the pic. It should be interesting to try it out though the fish that I find on my beach aren’t nearly as fresh looking as the specimen shown here and I’d wager they’re more aromatic as well. Fortunately, my grandson is at the age where gross and smelly just makes the activity all the more desirable. :-)

  20. #25 indeed they do.

    My favorite is when they use trace elements, like minute amounts of pollutants, or even temperature changes to be able to tell where the fish lived during their lives. Sadly, most fish are not yet wearing GPS devices, which would make them much easier to manage.

  21. Suggest a revision of the words “and maintain inertia”.

    From the essay:

    “…they orient us in the world, since they work as tiny inertial references…”

    I maintain inertia mostly on weekends.

  22. This is so cool — many years ago, I bought a pair of earrings somewhere near the ocean (Monterey?), and when I asked what they were made from, the vendor said “the ear bones of a cod fish.”

    See picture:

    It’s not that I didn’t believe her – I did – but I didn’t know that fish even had earbones…And this was way, way before you could look up something like this on Wikipedia!

  23. “Snapping (and presumably mantis) shrimp can also generate acoustic pressures in excess of 200 db.”

    Well that’s 200. 230 is 1000 times as loud as 200. From Googling, the only things I found at 230 decibels were massive towed navy sonar arrays (which drown out whales’ communication and echolocation dozens of miles away), and the hypothetical sound standing under a Saturn V.

    (Not trying to be nitpicking. It was just an incredible claim.)

    1. PlayGhost has gone to that undiscovered bin from whose bourn no spammer returns.

  24. I have collected / murdered probably thousands of fish for their otoliths (for Science!). Definitely some Macbeth moments afterward trying to wash your hands of the guilt (and the fish goo).


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