RESULTS 



Tissues from 134 specimens of Cvassostvea gigas from four sites were 

 examined for histopathologies over five sampling trips. From the speci- 

 mens collected, tissue samples of 131 adductor muscles, 127 stomach/ 

 intestines, 129 digestive glands, 130 gonads, 134 gills, and 130 mantles 

 were examined for a total of 781 tissues out of a possible 804. 



A total of nine types of pathologies were found with an incidence 

 of 241 occurrences (Table 1). Five-hundred and ninety of the 781 (75.6%) 

 tissues examined were free of pathologies; or, 191 of the 781 (24.3%) 

 tissues examined bore one or more pathologies. Of the 241 pathologies 

 found, 77 (32.0%) were various types of symbioses, while 164 (68.0%) 

 cases apparently were not correlated with symbioses. Table 2 summarizes 

 the distribution of pathologies among the tissues examined. Adductor 

 muscle had the lowest incidence (3.8%). Digestive gland tissue had the 

 highest incidence (23.9%) followed by gill (22.0%), mantle (21.4%), gut 

 (17%), and gonad (11.9%). The number of tissues with pathologies was 

 nearly evenly distributed among the collecting sites. Oysters from 

 reference stations had a higher incidence of lesions, particularly in 

 gonad and gill, than oysters from oil-polluted sites. Thirty percent of 

 the oyster tissues from both Aber Wrac'h and Aber Benoit bore one or more 

 pathologies. Forty percent of the tissues from Rade de Brest and lie 

 Tudy combined contained one or more pathologies. 



Overall, mantle bore the lowest number of pathology types (3) while 

 digestive gland contained the most types of pathologies (9) followed by 

 gut (7), gill (6), gonad (5), and muscle (4). 



Pathologies and their distributions among organs and sites are 

 described below. 



1. Muscle . - Muscle tissues were examined from 131 C. gigas. 

 Samples for microscopic examination were dissected from the adductor 

 muscle and both fast and catch muscles were examined when possible. 

 Generally, two tissue samples were taken from each muscle and oriented 

 to give both longitudinal and cross sections. 



Histopathologies occurred in 4.6% (6 of 131) of the muscle samples 

 examined. There were a total of 9 incidences of. the three pathologies 

 described below. Muscle from reference stations contained the widest 

 variety of pathologies. No pathologies were found in muscles from Aber 

 Benoit. 



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