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ange. Dominant tissue-free amino acids in all samples were taurine
(TAU) , glycine (GLY) , proline (PRO) and alanine (ALA) . In all samples
from all collections and stations, taurine concentration was maintained
nearly constant (range of means, 57.4 - 68.7 uM/g wet weight). There
was a trend for glycine a.nd asp ar tic acid concentrations to be lower
in adductors of oysters from the two oil-contaminated Abers than in
adductors of reference oysters. The result was that free taurine :glycine
molar ratios (a recommended index of pollutant stress) were
significantly higher in adductor muscles of oysters from Aber Benoit
and Aber Wrac'h than in adductors of reference oysters in all but one
instance (Table 27). Jefferies (1972) has suggested that taurine:glycine
ratios higher than about 2.0 in mollusc tissues may be a good
index of stress. As indicated above, the high taurine: glycine ratios
are attributed almost exclusively to a decrease in free glycine concentration.
This, in turn, may be attributed to poorer nutritional status
or altered patterns of amino acid metabolism in oil-stressed oysters.
Similar patterns were observed in free amino acid profiles and
concentrations in skeletal muscle of plaice (Table 28-32). Total free
amino acid concentrations were much lower in plaice muscle than in
oyster muscle, reflecting the well-developed capability of plaice to
regulate body fluid concentration hypoosmotic to the ambient seawater
medium. As in oyster muscle, taurine, glycine and alanine were the
dominant free amino acids in plaice muscle. Concentrations of several
free amino acids were statistically significantly different in muscle
of plaice from Aber Benoit and/or Aber Wrac'h than in muscle of reference
plaice. However, there was no consistent pattern of change. Free
glycine concentration was lower in muscle of plaice from the Abers than
in muscle of plaice from reference stations in December 1978 and August
1979. In February and June 1980, free taurine concentration in muscle
of Aber Wrac'h plaice was lower than in muscle of reference fish. In
February 1980, it was higher. Despite these as yet unexplained variations,
in seven out of nine cases where comparative data were available,
mean free taurine: glycine molar ratios in muscle of plaice from Aber
Benoit and Aber Wrac'h were statistically significantly different from
ratios in muscle of reference fish (Table 33)
. Because of seasonal
variations in free taurine: glycine ratios in muscle tissue of oysters
and plaice, it is important when using this parameter as an index of
stress to compare values for pollutant- impacted and reference animals
collected at the same time from nearby locations.
Several biochemical parameters were evaluated as potential indices
of pollutant stress in oysters and plaice from oil-contaminated Aber
Benoit and Aber Wrac'h. Values of some of these parameters were
statistically significantly different in populations from the
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