14 
BULLETIN - OF THE BUREAU OF FISHERIES 
daily. It thus appears that under different conditions oysters behave decidedly 
differently. 
Various factors may have been concerned in the low records, such as salinity 
variations, temperature, hydrogen-ion concentration, or the specific salts comprising 
the dissolved load of the water. This last will be discussed in a forthcoming paper. 
SUMMARY 
In the experiments with Olympia oysters it was indicated that it is not so much 
the existing temperature of the water which determines how long the shells remain 
open as it is the changes in temperature which occur. Falling temperature causes 
the shells to close, while opening follows a rise in temperature. The sensitivity of the 
Olympia oyster to temperature changes varies in an inverse manner with the general 
water temperature, within the range of 5° to 17° C. The latter temperature appears 
to be close to the optimum, for at this temperature slight changes (2° C.) produce 
almost no effect on the proportion of time the shells remain open. At temperatures 
of 4° to 6° C., when the oyster is hibernating with respect to gill activity, the shells 
do not remain constantly closed, but the oysters are highly sensitive to temperature 
change, and at such temperatures consequently remain closed a relatively high per- 
centage of the time. 
Because of this type of changing sensitivity and the diurnal temperature wave, 
with its trough at 6 to 7 a. m. and crest at 3 to 4 p. m., the curve of shell activity is 
of the same shape as the temperature wave, having trough and crest at the same times. 
Similar diurnal curves of the shell activity of eastern oysters are presented, 
without temperature data, and it is suggested that the conclusions with regard to 
the Olympia oyster also apply in principle to the eastern variety. 
The length of time which oysters remain open depends upon temperature and 
other factors. The Olympia oysters were open over 20 hours per day, while eastern 
oysters at Beaufort, N. C., averaged between 10 and 14 hours per day open, as con- 
trasted to Nelson’s (1921) figure of 20 hours and Galtsoff’s (1928) of 17 hours and 7 
minutes for oysters in New Jersey and Massachusetts, respectively. 
LITERATURE CITED 
Galtsoff, Paul S. 
1928. Experimental study of the function of the oyster gills and its bearing on the problems of 
oyster culture and sanitary control of the oyster industry. Bulletin, United States 
Bureau of Fisheries, Vol. XLIV, 1928 (1929), pp. 1-39, 13 figs. Washington. 
1931. The effect of sulphite waste liquor on the rate of feeding of Ostrea lurida and 0. gigas. 
In Effects of pulp mill pollution on oysters, by A. E. Hopkins, Paul S. Galtsoff, and 
H. C. McMillin. Bulletin, United States Bureau of Fisheries, Vol. XL VII, 1931. (In 
press.) Washington. 
Hopkins, A. E. 
1931. The effect of sulphite waste liquor on the oyster ( Ostrea lurida ). In Effects of pulp 
mill pollution on oysters, by A. E. Hopkins, Paul S. Galtsoff, and H. C. McMillin. Bul- 
letin, United States Bureau of Fisheries, Vol. XL VII, 1931. (In press.) Washington. 
Nelson, Thurlow C. 
1921. Report Department of Biology, New Jersey Agricultural College Experiment Station for 
the year ending June 30, 1920 (1921), pp. 317-349, 6 figs,. 5 pis. Trenton. 
