ADAPTATION OF OYSTER TO CHANGES IN SALINITY 
363 
3. Recovery, or adaptation, following a rise in salinity is very rapid as compared 
with adaptation following the same change in the opposite direction. The former 
may require a few hours, while several days may be necessary in the latter case. 
4. The rate of adaptation depends upon the degree of change and upon the 
extent of departure from optimum salinity. It is probable that, as the salinity departs 
further from the optimum, adaptation would never be so complete that water would 
be pumped at the normal rate. 
5. Because of the great variability in activity of the gills and in degree of openness 
even under conditions of constant salinity and temperature, the results do not justify 
exact statement of the optimum salinity. However, the optimum is probably not 
greatly different from that of ocean water, for salinities between about 25 and 39 
parts per mille appear to produce similar effects. 
6. While the oyster will tolerate a salinity as high as 39 parts per mille, higher 
than that of pure ocean water, and pump at the maximum rate, a salinity of 56 parts 
per mille, is definitely too high for it to tolerate. 
7. As the salinity is reduced below about 20 parts per mille the oyster becomes 
increasingly sensitive. A longer time is required for adaptation to relative stability, 
and it is probable that the rate of pumping would never become as high as that 
observed at salinities of about 28 parts per mille. 
8. The lower limit of tolerance, or the minimum salinity at which water is 
pumped effectively, is between 10.5 and 13 parts per mille. At the former salinity 
almost no water is pumped, although the valves remain well open. 
9. At a salinity of about 13 parts per mille little water is pumped, even after 
several days are allowed for adaptation, but recovery to normal activity occurs 
readily following restoration of a higher salinity. 
10. A salinity as low as 10.5 parts per mille produces a harmful effect, after 
which recovery in water of high salinity is extremely slow. Tins effect appears to be 
within the gill mechanism rather than the adductor muscle. 
11. A change to a lower salinity appears to affect the gill mechanism primarily, 
while following a rise in salinity the adductor muscle tends to hold the valves closer 
together than normally, resulting in a slower rate of pumping even though the gills 
may be well adapted. 
LITERATURE CITED 
Churchill, E. P., Jr. 1920. The oyster and the oyster industry of the Atlantic and Gulf coasts. 
Appendix VIII, Report, U. S. Com. Fish., 1919 (1921), 51 pp., 29 pis., 5 figs. 
Elsey, C. R. 1935. On the structure and function of the mantle and gill of Ostrea gigas (Thun- 
berg) and Ostrea lurida (Carpenter). Trans., R. S. C., Section V, Biological Sciences, pp. 
131-160, IV plates, 1 fig. 
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. Bull., U. S. 
Bur. Fish., vol. XLIV, pp. 1-39, 12 figs. 
Hopkins, A. E. 1931a. Temperature and the shell movements of oysters. Bull., U. S. Bur. 
Fish., vol. XLVII, pp. 1-14, 10 figs. 
Hopkins, A. E. 1931b. 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. Bull., U. S. Bur. Fish., vol. XLVII, pp. 125-162, 38 figs. 
Hopkins, A. E. 1933. Experiments on the feeding behavior of the oyster, Ostrea gigas. -Jour., 
Exper. Zook, vol. 64, pp. 469-494, 10 figs. Philadelphia. 
