Fish are cleaned and dressed at market as ordered, but need additional cleaning before cooking. Remove scales which have not been taken off. This is done by drawing a knife over fish, beginning at tail and working towards head, occasionally wiping knife and scales from fish. Incline knife slightly towards you to prevent scales from flying. The largest number of scales will be found on the flank. Wipe thoroughly inside and out with cloth wrung out of cold water, removing any clotted blood which may be found adhering to backbone. Head and tail may or may not be removed, according to size of fish and manner of cooking. Small fish are generally served with head and tail left on.
With sharp knife remove fins along the back and cut off a narrow strip of skin the entire length of back. Loosen skin on one side from bony part of gills, and being once started, if fish is fresh, it may be readily drawn off; if flesh is soft do not work too quickly, as it will be badly torn. By allowing knife to closely follow skin this may be avoided. After removing skin from one side, turn fish and skin the other side.
Clean and skin before boning. Beginning at the tail, run a sharp knife under flesh close to backbone, and with knife follow bone (making as clean a cut as possible) its entire length, thus accomplishing the removal of one-half the flesh; turn and remove flesh from other side. Pick out with fingers any small bones that may remain. Cod, haddock, halibut, and whitefish are easily and frequently boned; flounders and smelts, occasionally.
Clean, skin, and bone. A piece of fish large or small, freed from skin and bones, is known as a fillet. Halibut, cut in three-fourths inch slices, is more often cut in fillets than any kind of fish, and fillets are frequently rolled. When flounder is cut in fillets it is served under the name of fillet of sole. Sole found in English waters is much esteemed, and flounder is our nearest approach to it.