The hydrocarbon data demonstrate convincingly the dramatic 

 differences in patterns of petroleum hydrocarbon contamination of 

 oysters and plaice from the same oil-contaminated Abers. Oysters 

 contained high concentrations of alkanes, dominated by low molecular 

 weight compounds, while in plaice, the dominant alkanes in liver 

 samples were the higher molecular weight compounds. Oysters contained 

 abundant petrogenic and pyrogenic aromatic hydrocarbons spanning a wide 

 molecular weight range. Plaice on the other hand contained little 

 true aromatic hydrocarbon. These differences undoubtedly reflect the 

 markedly different capabilities of bivalve molluscs and teleost fish 

 to metabolize and actively excrete petroleum hydrocarbons. Most 

 teleosts studied to date have a highly active and inducible cytochrome 

 P-450 mixed function oxygenase system capable of converting aromatics 

 and some aliphatics to polar and more easily excreted matabolites 

 (Neff, 1979). This enzyme system is absent altogether or present at 

 very low activity in bivalve mollusc tissues. 



Biochemical Indices of Stress 



Total lipid concentration in tissues of oysters and plaice, deter- 

 mined in connection with hydrocarbon analyses, showed no consistent 

 patterns in relation to station or season (Tables 17-18). In June 1980, 

 but not at other sampling times, oysters from the two oil-contaminated 

 Abers contained 2-3 times as much lipid as oysters from the reference 

 station. It is quite possible that this is related to differences 

 between reference and Aber oysters in state of reproductive ripeness, 

 and not directly to oil- induced effects. 



Heniolymph glucose concentrations in oysters were low, highly 

 variable, and showed no relationship to station (Table 19). No statis- 

 tically significant differences were noted in values for reference and 

 Aber oysters. There was a trend at all stations toward increasing hemo- 

 lymph glucose concentration between December 1978 and August 1979. 



Some patterns did emerge in serum glucose concentrations of plaice 

 (Table 20). In December 1978, April 1979 and August 1979, with one 

 exception, serum glucose concentrations of plaice from oil-contaminated 

 Aber Benoit and Aber Wrac'h were lower than values for reference plaice. 

 Two of these differences were statistically significant. The collecting 

 technique (otter trawl) is highly stressful, and maximal hyperglycemic 

 stress response occurs rapidly in fish (Thomas et al., 1980). The 

 data suggest, not that Aber plaice were less stressed than reference 

 plaice, but that they had become refractory — perhaps due to chronic 

 stress — to capture-induced hyperglycemia. Inability to respond bio- 

 chemically to stress has been demonstrated in plaice held in the 



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