0023-6152

AA00697606

4486554

To develop a biomonitoring system to assist in the early detection of oxygen–deficient water in aquaculture settings, we conducted laboratory and field experiments using shell valve movements (SVMs) of Pacific oysters (Crassostrea gigas). Typical patterns of SVM showed that closing was quick (closing time ~1 sec), whereas opening was slow (opening time ~10 min). Under normal conditions, the SVMs averaged 6 ± 3 times/h. In a laboratory test, however, SVMs responded immediately when the dissolved oxygen concentration decreased and increased to 30 ± 17 times/h. When the dissolved oxygen concentration was only 2.0 ppm, all experiments recorded no SVMs; instead, the shells remained closed. Abnormally high or low rates of SVM were a regular occurrence under hypoxic and anoxic conditions. In field experiments, oyster shells remained closed in hypoxic water, but the rate of SVMs rapidly increased before and after exposure to hypoxic water, just as in the laboratory experiment. Thus, the observation of rapid SVMs or no SVM might serve as a biomarker of abnormal conditions, such as oxygen–deficient water.