Fish is similar to white meats such as veal and chicken, but has a high percentage of refuse (1/3 - 2/3) and is from 1/3-1/2 water. This leaves little solid in any given weight, but as fish is relatively low in cost, it is not expensive protein (building) food. It is as a digestible protein food that it is valued. Salts of fish do not vary significantly from those of meats, as is often claimed.

The composition of fish differs rather widely. Though, this is most noticed in the fat, it is marked in the amount of protein. Protein in fish is partly gelatin. Fish with less than 2% of fat (cod, haddock, whitefish) are most digestible. Those with more fat, but less than 5 % (mackerel, halibut), are palatable, as are also those with even more than 5 % (salmon, herring, bluefish), though these are much less digestible. The flavor of fish is affected by their food and the conditions under which they live. In salting and preserving, fish, like all meats, lose water, so have higher per cent of nutrients in this form.

Only when fresh can fish be eaten with even safety; only near the source of the supply is fish food advisable. No food decomposes more quickly or dangerously. Toxic substances (ptomaines), resulting from decay changes, are produced in stale fish; these act as poisons in the human system. Fish should always be kept on ice and invariably used promptly. When fish has been frozen it should be thawed in cold water and cooked at once. It keeps even less well than when fresh.

Thorough cooking of all fish is imperative; the danger from parasites is thus averted. Such sea fish as sea-shad require cooking by a method that permits escape of oil. After cooking, all fish should be opaque, not clear. This does not require exceedingly high temperature. Boiling is, however, less desirable than dry heat of temperature even a little below the boiling point of water, but sufficiently continued.