70 
BULLETIN OF THE BUREAU OF FISHEBIES 
pH was seldom below 8, but in the bayou in August it rose to nearly 9, due probably 
to algal growth. The pH of the water was not observed to have any particular 
significance with regard to the spawning and setting of oysters. 
OBSERVATIONS ON SETTING 
It has been established by Prytherch (1929) that the usual period of larval 
development, from the time of spawning until the larvae set, is about 15 days. By 
means of this knowledge he was able to predict in Long Island Sound the beginning 
of setting by determining the time when spawning started. Where conditions remain 
constantly favorable, such a method of obtaining set economically maybe employed, 
but in Galveston Bay no such relationship between the times of spawning and setting 
JULY AUGUST 
Figure 12.— Chart showing intensity of setting of oyster larvae and a few salinity determinations at Hanna 
Reef, East Bay, from May to August, inclusive 
was found to obtain. The oysters started spawning at the end of March, but no 
appreciable set was obtained at any place until the middle of May, after nearly 
two months had elapsed. 
The problem of obtaining adequate set is the most important one in the industry, 
and an attempt was made to determine when periods of setting might be expected 
in order that they be taken advantage of to procure seed oysters. Obviously the 
time of spawning had little bearing upon the setting time in Galveston Bay, for 
factors other than the normal length of the larval period appeared to influence the 
maturation of the larvse. 
In order to determine as closely as possible the time when setting takes place, 
wire bags of shells were placed in favorable positions in the bayou (fig. 5, Stations I 
and II), in West Bay (fig. 4, Station III), and in East Bay (fig. 3, Station IV). At 
each station bags were placed both on top of the natural reef at approximately low- 
tide level or a few inches above and at the edge of the reef in 2-4 feet of water at low 
tide. Each bag of shells was numbered and the time and position of planting recorded. 
At intervals of one to three weeks new bags were planted in each place and repre- 
sentative ones of those that had been exposed in the water were brought to the 
