Forest Preserve District of Cook County (Illinois)
Nature Bulletin No 552-A February 1, 1975
Forest Preserve District of Cook County
George W. Dunne, President
Roland F. Eisenbeis, Supt. of Conservation
****:SHRIMP
Here in the Middle West we are a thousand miles from the Gulf of
Mexico where the shrimp boats haul their nets. Once a rare delicacy
practically unknown in the average American home, the shrimp has
become one of the most common sea foods on our inland markets. In
cities and towns and along highways we see dozens of neon signs
advertising "French Fried Shrimp". This has come about because rich
new shrimping grounds have been found where American fishermen
with their improved otter trawls can scoop up this "pink gold" on a large
scale. And, gold it is, because they receive 65 million dollars or more
annually for their catch -- more than for salmon, tuna, oysters or any
other sea food. Annually Chicago wholesale dealers, alone, distribute
more than 15 million pounds of shrimp tails.
A favorite pastime along the coasts of our southern states is to catch
shrimps at night with casting nets. They jump like grasshoppers and
their eyes glint orange by reflected light. Few of us northerners have
ever seen a whole shrimp, much less a live one, because commercial
fishermen pinch off their heads as they are caught. Actually the "head"
of a shrimp is much more than a head. This shell-encased head includes
the internal organs, as well as the attachments for the legs, eyes and
other forward appendages, and the very long antennae or whiskers. This
leaves only the meaty tail and a part of the intestine called the "vein".
The shell is very thin and, in life, translucent with faint tinges of blue,
green or gray. Only after they have been boiled do they turn "shrimp
pink".
The shrimp is a crustacean related to the crayfish, lobster and crab. Like
them it has five pairs of legs but, unlike them, the first pair is not an
enlarged pincer or heavy claw. In water, they have three means of
locomotion: walking or climbing with the legs, darting backward by
flipping the scoop-like tail, or gliding slowly forward by the rhythmic
paddling of several pairs of swimmerets under the tail. They feed on
dead plant and animal matter.
Adult shrimps of different kinds range in body length from a little over
an inch to eight inches or more. Most species live in salt water or
brackish water, but a few kinds live entirely in fresh water. The females
of these latter kinds carry their eggs under the tail as crayfish females
do. These hatch into young that look like miniature replicas of the
adults.
Infant shrimps of marine species, in contrast, get no parental care and
go through a long series of transformations before they are the least bit
shrimp-like in appearance. The female of the common edible shrimp
releases enormous numbers of microscopic eggs -- a half million to a
million of them at a time -- in the waters of the Gulf. These develop into
tiny mite-like larvae that drift at the mercy of ocean currents and suffer
enormous losses at every stage. At first they have unsegmented bodies,
a single simple eye and three pairs of rudirnentary appendages. With
each succeeding molt, new appendages are added until there are
nineteen pairs in all, the body becomes segmented, and it gets the two
compound eyes typical of adult crustaceans. Only a few reach the
nursery ground near shore where they grow rapidly. When nearly
mature they migrate back to sea and make the final change into full-
blown shrimps.
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