First of all, it's really important to chose a freshwater fish. As a fisherman, I caught the fish last night in lake Balaton.
To prepare the fish, remove all the fish-scales, the guts, tail, fin, pharyngeal teeth (only the carp has them - If you don't want to bother just throw away the whole head) and the eyes.
Wash them well.
We need 500g of the carp meat to make our pasta filling, so remove that amount.
Slice up the rest, chop the head into two pieces. Place them in a pot.