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.