>
>
> Besides, you could use non-numeric characters. A-Z, a-z, Smiley
> Face, Batman sign. Get you a good 100^10 easy. Handy if you
> want to tag fish, rabbits, beetles, ants.........


Fish are already tagged.

Fish hatcheries can use temperature variations to change the growth rate,
and give in effect, a "bar code" in the scales.  Good for tracking where
they end up, but not individualized.
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