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Comment by fb03 | Hacker News Reader

That is beyond amazing to me.

As a layperson in biology related stuff, I'd like to ask: How do scientists estimate the age of non-human animals?

Otoliths are calcium carbonate structures that form in the heads of fishes that help with balance and orientation. Humans actually have similar things in their ear canals, they just don't aggregate and it's more like sand.

These structured grow with the fish and seasonal changes in growth rate cause lighter and darker alternating bands, similar to tree rings. When prepared correctly, these bands can be viewed and counted inter s microscope.

Similar methods are used in fin rays and spines, scales, and vertebrae, although otoliths are generally considered the gold standard

Along with that, the more expensive method that scales a bit easier is DNA methylation: most vertebrates, including fish, have a strong correlation between the percentage of their genomes that has been methylated and the age. It's like r=0.99, the older, the more methylated. (however, artificially de-methylating doesn't make you younger)

So you can sequence these genomes and count. Definitely more expensive than digging out a tiny bone, but you can sequence a few hundred or thousand genomes at once.

Random example paper: https://www.nature.com/articles/s41598-023-36773-2

Thank you for the info, I will research more about this.

Look up Otoliths. It’s a bone in the ear of fish that is commonly used for aging.

Thank you for the info and the appropriate term. I will research more about this!

Time for some wikipedia deep dives!

For some fish, you can count the rings on their scales like a tree.

Thank you for the reply! Other repliers answered that I should look up "Otoliths", which is the bony structure in the ear canal of some fish that can be used to count these rings.

Awesome info, everyone

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