The main difference between fish from fresh water and those from salt water, as food, is that the salt-water fish are an important source of bromin and iodin in the diet, and are considered desirable because of the value of iodin in preventing goiter. Some of the most common salt-water fish are cod, haddock, halibut, smelt, mackerel, salmon, shad, herring, oysters, clams, scallops, lobsters, crabs, shrimps and prawns, and some terrapins. Fish as food may be divided into:

White Fish - Fish that have less than two per cent fat, examples of which are smelt, flounder, yellow perch, pike, pickerel, sea bass, cod and haddock.

Medium Fat Fish - Fish that have two to five per cent fat, examples of which are weakfish, brook trout, mullet, and white perch.

Fat or Oily Fish - Fish that contain five per cent or more of fat, examples of which are salmon, shad, herring, lake trout, bluefish, Spanish mackerel, butterfish, and eels.

Shellfish - Mollusks (oysters, clams, scallops and mussels) ; crustaceans (lobsters, crabs, shrimps, prawns, crawfish or crayfish) ; reptiles (frogs, terrapins and turtles. The reptiles really belong to a lower order of animal than fish, but as they spend some time in the water they are discussed in this chapter.).