Study on the mechanism of the large amount death of Corbicula japonica

为明确1997年真地湖日本小圆蚧大量死亡的机理，于1999年在不同种群密度的容器中进行了试验。结果表明，较高的密度会导致(1)死亡率增加，(2)滤过率降低，(3)耐氧能力降低。在较高种群密度（3000株/m^2 ~ 4000株/m^2）的容器中，在夏季发现粳稻大量死亡之前，果肉干重迅速下降。为了明确这些元素的价值，有效地检查了金银花的状况，2000年进行了一些实验。研究了岛根县金仔湖人工泻湖中日本刺参生长条件指数、滤过率和缺氧耐受性的季节变化。5 ~ 9月，虽然条件指数下降幅度较大，但滤过率和对缺氧条件的耐受性下降不明显。这说明人工泻湖为金盏花的生长提供了良好的条件。人工缺氧条件下粳稻的条件指数迅速下降。当状态指数降低率大于3%/d时，出现大量死亡。在大量死亡的情况下，过滤速率降低到0.1 l/ind以下。人力资源。这两个值的结合可为检验粳稻病况提供指导，并可有效预测大面积死亡。

To clarify the mechanisms of the large amount death of Corbicula japonica occurred in Lake Shinji in 1997, experiments were carried out with containers in different population densities of C.japonica in 1999. It revealed that higher density results in (1) increase of the death rate, (2) decrease of the filtration rate, (3) decrease of anoxic tolerance of the bivalve. Before the large amount death of C.japonica was recognized among containers of higher population density (3000 ind./m^2 4000 ind./m^2) in summer, the rapid decrease of the flesh dry weight was observed. To clarify the value of the elements effective to check the condition of C.japonica, some experiments were carried out in 2000. Seasonal changes of Condition Index, filtration rate and tolerance of anoxic condition were examined for C.japonica living in an artificial lagoon built beside the Lake Jinzai, Shimane Prefecture. Although the Condition Index reduced largely from May to September, the filtration rate and the tolerance of anoxic condition did not reduce so apparently. It indicates that the artificial lagoon was kept in a comfortable condition for C.japonica. The Condition Index of C.japonica kept in an anoxic condition artificially reduced rapidly. It appears that the large amount death occurs when the reducing rate or the Condition Index becomes larger than 3%/day. In these cases of large amount death, the filtration rate is reduced to under 0.1 l/ind. hr. The combination of these two values may provide a guide to check the condition of C.japonica and effective to predict the large amount death,