Development of methods of preservation of aquatic environment with probability of extinction

为保护日本珍稀蟹种日本大闸蟹，采用野外调查和室内实验相结合的方法，对九州岛基塔河日本大闸蟹的数量变化、栖息地特征及生长过程的影响因素进行了研究。研究结果表明：1)日本血吸虫主要分布在距河口4.8~6.4公里的潮汐河段，2)日本血吸虫数量呈下降趋势，观察期内日本血吸虫数量在356万~41万只之间，3)沙床水槽实验结果表明，日本血吸虫9 mm甲壳的最大临界牵引力为1.19Pa.4)日本血吸虫喜欢河床物质直径5~80 mm，水温20~25℃，盐度接近0~10的生境；5)平均每只雌蟹孵化的卵子数为710个；6)日本血吸虫卵孵化至少需要2个月；7)从第一个阶段到第二个阶段需要5天，从第二个阶段到第三个阶段需要9天。

In order to preserve Deiratonotus japonicus, a rare species of crab in Japan, field surveys and laboratory experiments were carried out to investigate factors which influence changes in number, characteristics of the habitat, and the process of growth of Djaponicus in the Kita River, Kyushu island. Based on the results, correlations of each factor and population density of D.japonicus were analyzed.Research results are as follows :1)D.japonicus mainly distributes in a tidal reach from 4.8km to 6.4km from the river mouth ;2)D.japonicus tends to decrease in number, and was in a range of 3,560,000 to 410,000 individuals at the observation period ;3)Experimental results in a flume with sand bed shows 1.19Pa of the maximum critical tractive force for 9mm of D.japonicus in carapace ;4)D.japonicus prefers habitat with 5 to 80mm of riverbed materials in, diameter, 20 to 25℃ of water temperature and near 0 to 10 of salinity ;5)The number of zoeae hatched from one female crab was 710 on an average ;6)it takes at least two months for D.japonicus' eggs to hatch ; and7)It takes 5 days to become the second stage of zoea from the first and 9 days to grow the third from the second.