Figure 1. — American or Eastern oyster, Crassostrea virginica, photographed to show its upper and lower shells. New 

 shell growth is clearly seen along the edges. The white tubes on the shells are some of the fouling organisms normally 

 associated with oysters. 



as low as 5.0 p.p.t,, although under such 

 conditions their behavior was often abnormal 

 and they did not grow. However, in water of 

 7.5 p.p.t. the oysters grew, but much more 

 slowly than at higher salinities. The lowest 

 salinity at which spawn of Long Island Sound 

 oysters will develop normally is about 7.5 to 

 10.0 p.p.t. However, some oysters with ripe 

 gonads which developed at an optimum salinity 

 of about 25.0 p.p.t. spawned when placed in a 

 salinity of only 5.0 p.p.t. 



Experiments also have shown that these 

 oysters can withstand sudden changes from 

 low to high salinity, and vice versa, without 

 serious injury. They fed and expelled true 

 feces within a few hours after the change. In 

 general, oysters accustomed to low salinities 

 stop feeding and close their shells at lower 

 salinities than oysters conditioned to live in 

 water of higher salinity. As a rule, changes 

 in salinity of oyster body fluids closely follow 

 changes in salinity of the surrounding water. 



The temperature range that oysters can 

 tolerate also varies greatly. For example, 

 in Long Island Sound the winter water tem- 



perature over the oyster beds may drop below 

 32° F., while during the warm part of summer 

 it rises to about 73° F. in deep water and as 

 high as 78° F. in inshore areas. Oysters in 

 certain shallow water areas of Chesapeake 

 Bay withstand seasonal temperature variations 

 from the freezing point in winter to 90° F. in 

 summer. In the Gulf of Mexico the annual 

 range of temperatures over the oyster beds 

 is from about 50° to 90° F. 



It is interesting that the oyster, living 

 between tidal levels, may be frozen solid in 

 winter; yet, if not disturbed, will thaw out 

 and survive upon being covered by water. 

 If a frozen oyster is shaken or dropped, 

 however, changes occur in the cells of its 

 body that lead to death of the moUusk. 



ANATOMY AND PHYSIOLOGY 



Various aspects of anatomy and physiology 

 of oysters are described in hundreds of arti- 

 cles written by different authors. This knowl- 

 edge, however, is very well summarized in 



