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Figure 9.- 



-Adult American oyster. Crassostrea virginica. set up for gamma-irradiation at the Brookhaven National Atomic Energy 



Commission Laboratory. 



have use in sterilizing highly selected strains of a 

 commercial hatchery to increase somatic growth and 

 to prevent competitor companies from breeding the 

 strain. Irradiation might be used commercially to 

 induce parthenogenesis in obtaining instant, one- 

 generation pure homozygous individuals. A mutant 

 larval form with a larger mouth could increase the 

 types of algae an oyster larva would find acceptable 

 as a food since the larva would then be able to ingest 

 larger sized algal cells. 



Gamma rays from a Cs'^^ source extending from 

 65 to 10.000 R administered to large, old wild adults 

 in 1 hr. and from 220 to 20.000 R administered in 1 

 and 2 hr to wild spat about 9 mo old were not suffi- 

 cient to establish an LD.^dfor C.viri^inica. The lethal 

 dose must be affected by the season of the year the 

 oysters are irradiated, as well as by size of the oyster 



and shell thickness. These oysters and spat were 

 irradiated in the spring of the year as they were 

 coming out of their winter dormancy. Germ-line 

 primordia were beginning active mitoses. 



Gross cytological study of the gonads of the 

 gamma-irradiated adults revealed that even the max- 

 imum dose of 10.000 R did not adversely affect the 

 production of gonadal material. Instead, the treated 

 group as a whole had roughly about 209? more 

 gonadal bulk than did the control group: also, there 

 were fewer sexually undifferentiated oysters in the 

 treated group. 



Spawning performance of the irradiated adults 

 was better than that of the controls. Some adult 

 oysters receiving the maximum 10.000 R spawned. 

 However, none of the ju\eniles receiving more than 

 8,000 R spawned. 



85 



