MATERIALS AND METHODS 



Oysters Crassostrea gigas were collected during five sampling trips 

 to France. Dates of these trips were December 1978, April 1979, July- 

 August 1979, February 1980, and June-July 1980. In Aber Benoit, oysters 

 were obtained from commercial oyster pare owners in St. Pabu and Prat Ar 

 Coum. Oysters from Aber Wrac'h were obtained from a commercial opera- 

 tion near Paluden. Aber Benoit oysters were not available in August 

 1979. Reference oysters were obtained from several places. None were 

 completely uncontaminated with oil. On the first two trips, December 

 1978 and April 1979, the oyster pare operator at St. Pabu had oysters 

 from the Rade de Brest (supposedly uncontaminated) which he was holding 

 for later sale. We used these as reference oysters. Subsequent hydro- 

 carbon analysis revealed that these oysters were as heavily contaminated 

 with petroleum as Aber Benoit oysters. They had probably become contam- 

 inated during brief holding in the contaminated water of the Aber, as 

 Michel and Grizel (1979) subsequently showed in transplant experiments. 

 On the third trip, August 1979, reference oysters were obtained from the 

 CNEXO mariculture field station at lie Tudy. On the fourth and fifth 

 trips, February 1980 and June 1980, reference oysters were obtained from 

 a commercial oyster pare owner on the Rade de Brest at Plougastel. As 

 soon as possible after collection, the oysters were shucked and the soft 

 tissues fixed whole in freshly prepared Helly's fixative. The visceral 

 mass was incised to insure rapid penetration of the fixative. After 

 fixation the oysters were washed, dissected into several organs or body 

 regions, dehydrated in ethyl alcohol and embedded in paraffin embedding 

 medium. Organ systems processed for histopathological examination 

 included: visceral mass (includes digestive tract, digestive gland, 

 kidney and gonad), gill, and mantle. Sections were cut a 6 ym with a 

 rotary microtome and stained with hematoxylin-eosin. All tissue blocks 

 and prepared microslides of oyster tissues were labeled, inventoried and 

 archived. 



Tissue sections were evaluated qualitatively. The qualitative pro- 

 cedures included a description of the average and limits of normal for 

 the histological status of each tissue. All histopathological lesions 

 were described in full. The incidence of different types of lesions in 

 each tissue was recorded. The incidence of different types of lesions 

 in each tissue was recorded. These data for the three populations (2 

 oil-contaminated stations and one control station) were compared. 

 Seasonal and temporal differences in the incidence of pathological 

 lesions were also recorded. A photographic record of normal tissue 

 histology and of all types of histopathological lesions was made and 

 archived. 



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