Valve closure responses of the Asiatic clam Corbicula fluminea exposed to cadmium and zinc

The valve movement patterns of immobilized Asiatic clams (Corbicula fluminea) were monitored during exposure to constant concentrations of cadmium (0.0, 0.1, 0.2, 0.3, and 0.4 mg 1−1) or zinc (0.0, 0.1, 0.3, 0.5, and 0.9 mg 1−1) for 24 h following a 24-h acclimation period. Data indicate that the duration of response was concentration dependent and toxicity related. Durations of periods with valves parted declined as the concentration of heavy metal increased. Behavior was consistent for both mean time to first closure following the initial exposure and mean time per valve parting episode over a 24-h exposure period. Mean time per valve parting episode during the 24-h exposure period ranged from ≃ 600 minutes for control trials to 36 and 69 minutes for the highest concentrations of cadmium and zinc tested, respectively. There was no association between durations of periods with valves sealed and solutions of cadmium; however, lengthening durations of periods with valves sealed coincided with exposure of clams to progressively more concentrated zinc solutions. In addition, Asiatic clams demonstrated a greater rate of response (decline in the duration of periods with valves parted) to progressively more concentrated solutions of cadmium than to comparable increases in the concentrations of zinc solutions.