Abstract
During the period of oxygen depletion in bottom waters of Mikawa Bay of Japan in 1998 and 1999, the mortality and the glycogen content were examined for the Manila clam Ruditapes philippinarum kept in stainless-steel cages in the bottom sediment of shallow waters. In two ex-periments conducted over 5 weeks and 6 weeks, respectively, no large increase in the cumulative mortality rate was found in the early phase despite the development of oxygen-deficient waters. With further deterioration in oxygen condition, however, the cumulative mortality rate reached 99% and 57% in the first and second experiment, respectively. The mean values of glycogen content were initially 41.7 mg/g and 39.6 mg/g, and were reduced significantly to 21.4 and 15.7 mg/g, respectively, at the end of the experiments. Ruditapes philippinarum kept in normoxic waters as a control did not show a large increase in mortality rate, nor a significant decrease in glycogen content. Thus, glycogen content seems to be an indicator of physiological condition of R. philippinarum exposed to oxygen-deficient waters.
