1G 
BULLETIN OF THE BUREAU OF FISHERIES 
this habitat is not sharply defined; some shrimp as large as 100 mm have been en- 
countered, but the majority are below 40 mm. 
We have no data on the growth in this earliest stage, but they first appeared in 
the Georgia commercial catch at an average size of 90 mm (70 to 105) in July 1931, 
and again in July 1932, 2 or 3 months after the beginning of spawning. The reactions 
that lead the larvae from the outside more saline waters to the brackish muddy-bot- 
tom waters favored by the young, or lead the young back to the waters of higher sa- 
linity where they first enter the commercial catch, have not been studied, although 
they must hold the key to an understanding of one of the most interesting phases of 
the shrimp life history. 
To compare with this picture just given of the spawning, larvae and young of 
Penaeus setiferus, we may review the findings of Ehrenbaum (1890) on Crangon 
( Crago ), Mortensen (1897) on Palaemon, and Kishinouye (1900a), Spaulding (1908), 
Gates (1910), and Yiosca (1920, Tulian 1920, 1923, and 1926) on Penaeus. Ehren- 
baum found that in the North Sea the ovigerous females of Crago and the small free 
swimming larvae are found only in the strongly salt water of the flats and about the 
offshore islands of the North Sea. Only very exceptionally are larvae or ovigerous 
females taken in the brackish waters of the estuaries. 
In sharp contrast, the young, measuring 5 to 10 mm, are found in great numbers 
from spring to late summer in the Dollart and Jade Rivers, far upstream in brackish 
water. From the percentage of ovigerous females found at different seasons, Ehren- 
baum concluded that there were two spawning seasons and that hatching occurred 
primarily in July and to a less extent in March. No additional support for the double 
spawning season has been presented by the later writers. 
In Palaemon fabricii, studied by Mortensen, the females spawn in deep water in 
May, the eggs hatching chiefly in June. As in Crago the larvae are pelagic and never 
appear in the brackish water of fjords or creeks. After a pelagic life of 3 to 5 weeks, 
the first young appear early in July. The young are found in the rapidly growing 
vegetation of the shallow water of little creeks and fjords. The larger females are 
said to lay a second batch of eggs shortly after the hatching of the first. In neither 
of these species has fertilization been observed. 
It will be seen that the distribution of the ripest females, the larvae, and the 
young in both these species agree with what we have observed in Penaeus. 
The data of Kishinouye (1900a) are of more interest because they deal with 
various Japanese species of Penaeus closely related to the forms we are studying. 
Unfortunately, the basis of his statements are not given in the English summary of 
his paper. He gives tables for sexual maturity in five species. The period of May to 
September, inclusive, contains all these mature seasons, although most are individual- 
ly shorter than this. In three species the males are said to be sexually mature 
throughout the year. The eggs ripen in spring and spawning takes place in summer 
and autumn. Kishinouye describes the spermatophores in several species. Eggs 
are said to be discharged from time to time as they ripen. He mentions finding the 
larvae in shallower water than that in which the spawning shrimp live but does not 
specifically describe the habitat of the young. 
The breeding season given by Kishinouye agrees in general with our findings. It 
is not true of the male of Penaeus setiferus that mature individuals are present at all 
times of the year, as he claims for certain species. We are very much inclined to 
doubt that in Penaeus setiferus spawning takes place from time to time as the eggs 
ripen; it is more likely that all the eggs are spawned at one time. 
