Figure 8.— Group of larvae of relatively uniform size, about 175 m, from a weU-kept culture. Note protruding umbo of 

 the larval shells, which is one of the characteristics that distinguish advanced larvae of the genus Crassostrea from 

 the larvae of most other genera of bivalves. 



fed Chlorella , the larval growth within 68° to 

 87° F. increased progressively with each in- 

 crease in tennperature. When given good food 

 at the latter temperature the larvae began to 

 metamorphose 10-12 davs after fertilization 

 (fig. 9). 



If oyster larvae are reared almost to the 

 stage of metamorphosis at 80° F. and then 

 transferred to water temperatures of 77°, 

 73°, 71°, 680, and 64° F., the intensity and 

 duration of setting of these different groups 

 are profoundly affected by water temperature. 

 For example, all larvae transferred to 77° F. 

 underwent metamorphosis and set within 8 to 

 10 days. Those kept at 73° F. required fronn 

 12 to 16 days to complete the setting. At 68° F. 

 the slowest growing larvae required 20 days 

 to set. At 64° F. the setting period was even 

 more prolonged. In Sonne instances fully ma- 

 ture oyster larvae grown at optimum tempera- 

 ture can set even if transferred to a tempera- 

 ture as low as about 55° F. In general, within 

 a certain temperature range the number of 

 spat obtained from a given number of mature 



larvae decreases as the temperature to which 

 they are transferred is decreased. This re- 

 duction, however, is not as drastic as might 

 be anticipated. Even when mature larvae are 

 transferred to a low temperature of about 

 64° F. about half as many larvae as at 77° F. 

 may eventually metannorphose. All this knowl- 

 edge obtained by laboratory experiments helps 

 us to understand the behavior of larvae in 

 nature and assists in the management of our 

 oyster resources. 



Effects of Salinity on Eggs and Larvae 



Experiments demonstrated that the optimum 

 salinity for development of eggs of Long Island 

 Sound oysters is about 22.5 parts per thousand 

 (p.p.t.). Nevertheless, sonne normal larvae 

 originating from these eggs developed in 

 salinity as low as 15.0 p.p.t. and as high as 

 35.0 p.p.t. At salinities lower than 22.5 p.p.t., 

 however, the percentage of eggs developing to 

 straight-hinge stage steadily decreased until 

 at 15,0 p.p.t. only 50 to 60 percent of the eggs 



15 



