Then cut down to backbone just above collarbone. Turn knife flat and cut flesh along backbone to tail, allowing knife to run over rib bones. Lift off entire side of fish in one piece, freeing fillet at tail. Turn fish over and cut fillet from other side. Pre-treating Fish are categorized as either fat or lean fish based on the amount of fat in their flesh.
Fat fish includes varieties such as mullet, mackerel, trout, tuna and salmon.
Lean fish includes flounder, cod, whiting, redfish, croaker, snapper, grouper, sheepshead and most freshwater fish. Before freezing, fish need to be pre-treated to improve the quality of the stored fish. Fat fish should be dipped for 20 seconds in an ascorbic acid solution made from 2 teaspoons of crystalline ascorbic acid to one quart of cold water to decrease rancidity and flavor change. Place a double piece of freezer paper or wrap between fish in a package to make separation easier. To prevent evaporation of the ice, wrap the container in freezer paper after it is frozen.