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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, determined
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 statistically
significant differences were noted in values for reference and
Aber oysters. There was a trend at all stations toward increasing hemolymph
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 biochemically
to stress has been demonstrated in plaice held in the
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