Yeah the stuff on the knife is scales, but the silver on the fish is just the skin. The scales are attached to that.
I’d be really surprised if you’re finding any fish in big supermarkets that still have scales, even on a whole fish but particularly on a fillet.
You will typically find skin on or skin off fillets, and depending on the fish recipes might instruct to cook them skin side down so you can have a nice crispy texture alongside the softer flesh.
Okay, fair enough. That’s not something I’ve ever encountered. Sorry my tone offended you - I wasn’t trying to be a dick.