Unless you plan to skin a fish, the first step is to remove the scales. Holding the fish by the tail, scrape off the scales from tail to head with a sharp knife or a fish scaler – a saw-toothed instrument.
Next cut along each side of the pectoral and pelvic fins and pull them free. Remove the dorsal and anal fins the same way. Leave the fins on if the fish is to be cooked whole.
To remove the viscera of a round fish, slit the belly from head to tail. Pull out the insides, then scrape loose any blood pockets with a knife. To gut a flatfish, make a small opening behind the gills. After cleaning, rinse the fish thoroughly.
To remove skin from a roundfish, make cuts around the head and tail and the length of the back; working the knife under the skin, pull the skin toward the belly; cut it off. Repeat on the other side. For a flatfish, slit the skin at the tail on the dark side.
Holding the skin with a paper towel or a cloth, pull it to and over the head, then down to the tail on the light side. Cutting steaks and filets A roundfish, such as salmon or cod, is generally used for steaks. It should weigh no less than 10 pounds. Using a very sharp knife, slice the fish crosswise into pieces at least 1 inch thick.
For filets, use fish that are not too bony-either flatfish or roundfish. To make filets from flatfish, place the skinned fish with the eyes up and cut lengthwise along the center to the bone. Inserting the knife horizontally between the flesh and bone on one side of the slit, cut the flesh from the ribs in short strokes. Repeat on the other side of the slit. Turn the fish over and cut two filets from the other side in the same manner.
To make filets from roundfish, slit along the backbone and across the tail.
Filleting a flatfish
Then slice through the backbone between the vertebrae directly behind the gills. Using short strokes, run the knife the length of the fish as close to the ribs as possible. Turn the fish over and slice the filet from the other side.