Benoit (average of 20 to 32) and Rade de Brest and lie Tudy (average 

 of 22 to 31). The differences were not statistically significant. 



CONCLUSIONS 



In general, oysters Cvassostvea gigas from all five collections 

 and all four sampling stations appeared to be extremely healthy as 

 determined by histopathological examination. Incidence of parasitic 

 infestation was very low, especially when compared to incidence of para- 

 sitism in C. vivginioa from the northwest Gulf of Mexico. The low 

 incidence of parasitism in C. gigas from Brittany may be due to the fact 

 that they are a recently-introduced mariculture species in the area. 

 There probably has not been enough time for their parasites to catch 

 up with them. According to Henri Grizell (personal communication), 

 parasitism and disease are increasing in these oysters. 



The most prevalent pathologic lesion in C. gigas from Brittany was 

 leucocytosis. In mollsucs, this condition is usually a response to 

 chemical or physical irritation. It is an inflammatory defensive response. 

 However, size and distribution of leucocyte populations varies greatly in 

 different mollusc species under different environmental conditions. C. 

 gigas generally seems to have more leucocytes than the closely-related 

 C. vivginioa. Thus, the extent to which observed leucocytoses in C. 

 gigas were normal or pathologic is uncertain. In any event, incidence 

 of leucocytosis was similar in oysters from oil-contaminated Aber Benoit 

 and Aber Wrac'h and from reference stations in the Rade de Brest and at 

 lie Tudy. 



Necrosis was observed several times but no definitive cases of 

 hyperplasia, neoplasia or other precancerous conditions was noted in 

 any of the four oyster populations. 



There were no consistent temporal trends in incidence of pathology 

 in the oysters from oiled and reference stations. Oysters collected in 

 December 1978, nine months after the spill, had an incidence of patho- 

 logical conditions similar to that in oysters collected in June 1980, 

 twenty-seven months after the spill. One difference that may have 

 obscured other effects was size. By June 1980, oysters which had been 

 in the Abers at the time of the spill had grown to very large size. 

 During the first year after the spill, there was little evidence of 

 growth in oysters from the two Abers. During the second year, growth 

 appeared normal or even accelerated. 



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