LIFE HISTORY OF THE COMMON SHRIMP 
7 
pods in which the eggs, well supplied with stored yolk, hatch into larvae correspond- 
ing to stages occurring late in the larval history of Penaeus. 
No further work was done until more than 20 years later at the Gulf Biologic 
Station, Cameron, La. In 1908 Spaulding and Guilbeau and in 1910 Gates reported 
on the shrimp. Facilities were not available at the Gulf Biologic Station for an inten- 
sive study of the shrimp; consequently these preliminary papers contain only brief 
observational notes on the behavior and a few scattered length measurements. 
Spaulding, whose observations were the most extensive, reports that larval shrimp, 
less than one half inch in length, were obtained in Calcasieu Pass in August and Sep- 
tember. These were similar in form to the adult, but a series of larval stages was 
not obtained nor was identification of the species possible. No females with devel- 
oped ovaries were taken, but from a study of the males and the time of appearance 
of the larvae he concludes that there is a single breeding season extending from the 
first of May to the last of July. He thought it possible that the eggs were laid in the 
Gulf but presents no direct evidence. The size at maturity is not established. 
In 1918 the Louisiana Department of Conservation began a more intensive study 
of the shrimp. This work was done by Percy Viosca and published partly under his 
name (1920) and partly under that of Tulian, who was then commissioner (1920, 1923, 
1926). Viosca’s findings are more extensive than his predecessor’s but it is to be 
regretted that none of the data upon which his conclusions were based is given in any 
of the publications. As a result it is impossible to evaluate his interpretations of the 
life history. He states that Penaeus setijerus spawns in the Gulf, chiefly on the evi- 
dence that sexually mature shimp are found only in outside waters. The young are 
said to live in the plankton of the Gulf until a size of 1% inches is reached. “By May 
reasonable numbers of baby shrimp appear in the shallow waters near the coast line 
and a large proportion gradually migrate into brackish water, all growing rapidly 
throughout the summer.” 
This is all the information toward a life history of Penaeus setijerus available in 
1930. 
The following is a bald summary of the life history as determined by the present 
work. 
The eggs are laid from March or April to August or September in the outside 
waters of the ocean or Gulf. The post-larval young beginning at a length of 7 mm 
are found in bays, creeks, bayous, and lakes in warm, shallow, brackish water with 
mud bottoms. The young grow rapidly and with increasing size gradually migrate 
to deeper water of greater salinity. 
During July at an average length of about 90 mm they enter the commercial 
catch, appearing first in the bays, creeks, and other “inside” waters and later outside. 
They continue in the fishery, furnishing all of the fall catch, with its peak in 
October, until the following spring and summer, when they spawn and disappear at 
the age of 1 year. By late fall they have reached a length of about 120 mm, which 
they maintain during the winter. Resuming growth in the spring, they show a rapid 
and striking differentiation in the size of the sexes and spawn at lengths of 130 to 
170 mm for the males and 135 to 190 mm for the females. Their fate is unknown, 
but their complete disappearance from the commercial catch is undoubted. 
The breeding season is characterized by (1) a development of the gonads; (2) a 
rapid differentiation in size between the sexes; (3) a difference in the behavior of the 
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