Yep. Long time ago, before digital cameras.
There are a few lakes that have them, typically very cold clear shield or mountains. And they usually taste great
Every once in a while someone pulls out a silver pike from a random spot. So I think in the right environmental conditions (no weeds to hide in), it’s an uncommon but not rare mutation, that can become an advantageous trait and be passed on at a higher frequency. Sort of like color phase bears.