76. Besides the varieties of fish that have already been considered, the
general term fish also includes SHELL FISH. Fish of this kind are
different in structure from bony fish, for they are acquatic animals
that are entirely or partly encased in shells. They include _mollusks_,
or _bivalves_, such as oysters, clams, and scallops, and _crustaceans_,
such as lobsters, crabs, and shrimp.
77. The popularity of the edible varieties of mollusks and crustaceans
mentioned depends largely on whether they can be easily obtained and
whether they are pleasing to the local or individual taste. As they are
found in salt rivers, bays, and other shallow salt-water sources, their
greatest use is among people living near the seashore, but they are much
favored where they can be procured in edible condition. They are not so
cheap as many other fish foods; that is, a certain amount of money will
not purchase so great a quantity of shell fish, lobster for instance, as
some of the well-known varieties of fish proper, such as halibut or
whitefish. Lobsters and crabs are usually more expensive than oysters
and clams; consequently, they are used more often to provide a delicacy
or to supply something more or less uncommon for a special meal.
78. Several precautions should be observed in purchasing shell fish. For
instance, crabs and lobsters should be purchased alive. They are usually
shipped on ice so that they will remain in this condition for some time,
and they are displayed on ice in the markets for the same reason. Such
shell fish should be kept alive until they are plunged into boiling
water to cook. Oysters and clams bought in the shell must also be alive
when purchased. A tightly closed shell indicates that they are alive,
whereas a slightly open shell proves that they are dead. If these two
varieties are bought out of the shells, the fish themselves should not
be accompanied by a great quantity of liquid. Considerable liquid is an
indication that the oysters or clams have been adulterated by the
addition of water. Formerly it was the custom to keep oysters in fresh
water, as the water they absorb bloats or fattens them. This practice,
however, has fallen into disfavor.
79. Shell fish lend themselves admirably to a large variety of dishes,
including soups, entrees, salads, and substitutes for meat dishes. They
possess a great deal of distinctive flavor, their food value is
comparatively high, and, provided they are in good condition and are
properly prepared, they are healthful and easily digested. It can
therefore be seen that shell fish have much to recommend their use.
There is considerable danger, however, in using any varieties that are
not perfectly fresh or freshly cooked. In the case of mollusks, or
bivalves, much harm has resulted from the use of those which have been
grown or bred in unsanitary surroundings. Because of these facts, it is
of the utmost importance that great care be exercised in selecting and
preparing shell fish.
80. COMPOSITION AND FOOD VALUE OF SHELL FISH.--In composition, the
varieties of fish included under shell fish do not differ greatly from
fish proper. Most of them, however, contain more waste and less of the
food substances than fish, so that their food value is somewhat lower.
Table IV will serve to give a good idea of the composition and food
value of the several varieties of shell fish, and in studying it, a good
plan will be to compare it with Table I, which gives the food value of
fish. As will be observed, protein forms a very large proportion of the
food substance of shell fish. Also, they contain more carbohydrates than
fish, the amount ranging from .4 to 5.2 per cent., which is in the form
of sugar. Although this amount is too small to warrant much
consideration as a supply of carbohydrates, it is mentioned because it
is an interesting fact.