Assessment of Hard Clam Siphon Extension Activity as an Indicator of Commercial Depuration Efficiency

The results of a number of field and laboratory studies on the development, growth, survival and distribution of the hard clam, Mercenaria mercenaria have helped to establish the general guidelines for deputation but have not linked microbial depuration ability to a potential physiological indicator such as siphon extension. Results from 1984 to 1986 indicate that on a number of occasions individual hard clams either failed to extend their siphons or exhibited very low activities during commercial deputation. Siphon extension was significantly different within corresponding months of different years with the exception of late summer and late winter, which were consistently months of low siphon extension activity. Prior refrigeration of clams generally increased siphon extension activity compared to those clams depurated immediately after harvest. The results of both field and laboratory studies indicate that siphon extension was correlated with viral deputation but not with Clostridium perfringens release. These data provide the first instance of experimental support for siphon extension activity as an important physiological indicator in determining the ability of deputation to effect a reduction of microbial pathogens in hard clams.