Filleting Fish
To fillet round fish (herrings, for example):
Slit the belly of the cleaned fish from head to tail.
Squeeze your forefinger and thumb tightly around the backbone, directly behind the head, and, keeping close to the bone, draw your fingers firmly to the tail.
To fillet large round fish (cod, for example):
Make a vertical incision behind the head until you reach the bone.
Turn the knife on its side and run it along the bone to the tail
To fillet flat fish (sole, for example):
Run a sharp knife along the central line of one side.
Lay the knife sideways tight to the bone, and slice to the edge and the tail, at the same time lifting the fillet free with the other hand.