494 MANN 



oysters, found a positive correlation between the two parameters 

 (r=0.69), but omitting the three highest values for glycogen 

 content reduced the rvalue to 0.38. Ingle's general conclusion was 

 that the relationship between these two parameters was poor, but it 

 is notable that the glycogen contents of the oysters used in the study 

 are very low (1 to 2% in most cases), and this probably is not a 

 representative sample. By contrast, Walne (1970) and Gabbott and 

 Stephenson (1974) found a good correlation in O. edulis between the 

 dry -weight/shell-cavity ratio (index 2) and a glycogen condition 

 index calculated as glycogen (g)/internal shell volume (ml) (P < 0.01 

 and P < 0.001, respectively). 



Despite the constraints involved in the use of each regressed 

 parameter, the present data suggest that any of these parameters can 

 be used as equally valuable indexes of condition in the bivalves 

 described here. Only further studies of other species of bivalves can 

 confirm or eliminate these general relationships, but it is indeed 

 reassuring to suggest that an easily affected volumetric or gravimetric 

 assay of condition could be equally as meaningful as a more complex 

 biochemical one. The use of physiological indexes, such as the 

 O/NH3 ratio, must await further investigation for a complete 

 assessment of value. 



In a more general context, the use of any index of condition to 

 predict the bivalve's ability to withstand stress must rest upon an 

 understanding of basic life processes in the animals. Despite many 

 decades of intensive research, there are still areas markedly depau- 

 perate in documentation. For example, Bayne et al. (1976) recently 

 noted changes in the taurine/glycine ratio in mussel tissue as a 

 response to temperature stress. A complete physiological explanation 

 of this phenomenon is not yet forthcoming, however, let alone an 

 explanation that incorporates the effect of environmental stresses. In 

 studies of the response of bivalves to thermal perturbation, further 

 research is required at both the laboratory and field levels. In this 

 respect the recent studies of Gonzalez and Yevich (1976) and Bayne, 

 Widdows, and Worrall (1977) serve as excellent examples of the use 

 of modern techniques to provide evidence of thermal stress at the 

 biochemical, physiological, and cytological levels and will undoubt- 

 edly stimulate similar studies in the near future. 



ACKIMOWLEDGMENTS 



The research reported here was completed under grants from the 

 NOAA Office of the Sea Grant 04-6-158-44106 and the Jessie Smith 

 Noyes Foundation. 



