range. 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 concen- 

 tration. 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 refer- 

 ence 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 varia- 

 tions, 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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