SHELL MORPHOMETRY AND TISSUE CONDITION OF AMBLEMA-PLICATA (SAY, 1817)FROM THE UPPER MISSISSIPPI RIVER

We examined shell length-weight relationships and shell shape in the u nionid Amblema plicata (Say, 1817) from Pool 10 through Pool 26 of the upper Mississippi River. There were differences in both the intercept s and slopes of the relationships between size and other measured char acteristics among the various pools examined. There was a much greater degree of variability in the tissue related factors than in any of th e shell factors. There were no apparent upstream-downstream trends in any of the dependent variables. We also found that the shell can conta in a significant amount of organic material and the percentage of orga nic material varied considerably, particularly in larger mussels. This indicates the need to consider the shell in studies of the energy dyn amics of unionids. Tissue condition varied with mussel size; larger mu ssels had proportionally lighter shells and thus higher condition indi ces than smaller mussels. Because of the significant intra- and inter- pool variability in shell and tissue parameters which we observed, we urge that biomass estimates based on shell length-weight regressions f or this and other species should be based on empirical relationships o bserved for the particular population under study rather than from lit erature values.