Read the regs on the Salmon.

Do you wonder why dorsal fin height is listed as a way to identify hatchery fish?

If they aren't clipping dorsals, then why would their fins be less than 2 1/8" high, or not there at all?

They rub their dorsals off, but their tails and ventral fins aren't worn? Do they swim upside down?

I'll just say that if I'm wrong, it wouldn't be the first time. ;\)
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She was standin' alone over by the juke box, like she'd something to sell.
I said "baby, what's the goin' price?" She told me to go to hell.

Bon Scott - Shot Down in Flames