Fish skull thingies

June 12, 2007 8:18 PM

Icthyoid anatomy question: what are these things inside fish skulls?

When I pick apart the skull from a whole fish to get at the last tasty meat bits, I frequently find a pair of hard brittle pieces sitting just behind the fish brain, which don't seem to be attached to anything. These pieces are different shapes and sizes depending on the fish species, and are harder and more brittle than fish bone - actually they seem to have the same texture as tooth enamel or seashells, and each pair is exactly symmetrical, so I don't think they're calcium deposits or somesuch. Anyway what are these things, and what are they for? Do other vertebrates have them, and I'm only finding them in fish because that's the vertebrate skulls I'm most likely to have access to?

posted by casarkos to science & nature (8 comments total)

Otoliths.
posted by fish tick at 8:24 PM on June 12, 2007

I can't believe I know this, but they are ear bones. They are floating bones that are not attached to anything; they sit in a pool of liquid in the ear canal and transmit vibrations. The fish use them to track school movements and the actions of prey.

At one of my jobs we used to split codfish as a demonstration, and we would pierce the ear cavities and bring out the ear bones to show. They are beautiful indeed, like little feathers made of bone. The Gloucester fishermen used to bring them home to their girlfriends, and they also brought the eye-lenses home for kids to use as marbles.

And it is trendy, at this job, to have someone make the earbones into earrings for you. I've got a pair.

I know, it's weird.
posted by Miko at 8:37 PM on June 12, 2007 [1 favorite has favorites]

Here they are. Awesome; I never knew the word 'otoliths'.
posted by Miko at 8:38 PM on June 12, 2007 [1 favorite has favorites]

The neatest part is that you can tell how old the fish was from the rings on the bone. Fish can live to be very, very old. (As a vegetarian, I wish one could just ask the fish how old it is, but so it goes.)
posted by lemuria at 8:47 PM on June 12, 2007

Damn you people are fast and amazing. Thanks!
posted by casarkos at 8:56 PM on June 12, 2007

I know at least that in northern Europe, it is popular to eat carp for New Year's dinner. Some considered it good luck if you find the otolith. Some people dry them out and stick them in their wallet with the idea that it will bring them money.
posted by chillmost at 12:56 AM on June 13, 2007

It wasn't good luck for the carp, you know.
posted by mendel at 6:13 AM on June 13, 2007

Amphibians like salamanders have them as well. We used to enjoy asking the students about that one in the anatomy class - but it was damn hard to put a pin in the otolith without breaking it.
posted by caution live frogs at 6:45 AM on June 13, 2007