To scale the fish, hold it buy the tail and use the back of a knife to scrape towards the head. Remove the gills, by placing the fish on its back, open the gill flap, gently pull the gills between the flap, cut and discard. Repeat on other side of fish. Trim off the fins, using a pair of scissors. Make a slit in the stomach and remove all of the entrails. Rinse the whole fish thoroughly under cold running water.
Make a cut behind the head, cutting into the flesh with clean sweeping strokes, as close to the backbone as possible, moving towards the tail. Repeat with other fillet.
Boning - Herrings, etc.