From Cookipedia(Redirected from Descale)
Any fishmonger of repute will descale as well as gut and clean any fish you buy if you ask, this includes supermarkets.
However, descaling is pretty easy to to yourself:
Use a sharp knife. Remove the fins. Hold the tail and run the flat of the knife 'the wrong way' down the body of the fish a few times. I find this is best done under cold running water as it washes away the scales as they are removed. Give it a good rinse once you're finished and that's all there is to it.
We have got a strange device for de-scaling fish, but to be honest, a knife is just as good.