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

为弄清1997年神济湖河口河谷大批量死亡的机理，于1999年在不同密度的河口河口进行了容器试验。结果表明，密度越高，双壳类死亡率越高，滤水率越低，耐缺氧能力越差。在夏季种群密度较高(3000尾/m~2,4000尾/m~2)的容器中发现日本血吸虫大量死亡之前，肉质干重迅速下降。为了弄清有效元素在检查日本血吸虫状况方面的价值，我们于2000年进行了一些试验。在岛根县金仔湖边建造的人工泻湖中，对日本对虾的条件指数、过滤速率和耐缺氧能力的季节变化进行了研究。虽然条件指数在5~9月有较大幅度的下降，但过滤速率和对缺氧条件的耐受性并没有明显下降。这表明，人工泻湖对日本对虾来说是处于舒适状态的。人工缺氧条件下，日本对虾的状态指数迅速下降。当减少率或状态指数大于3%/天时，出现大量死亡。在大量死亡的情况下，滤速降至0.1%L/英寸以下。人力资源。这两个值的结合可以为检查日本血吸虫的病情提供指导，并有效地预测大量死亡。

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,