| In China,there are approximately 20,000,000 acres of low-lying salt marshes that are unsuitable for planting crops.Of these marshes there are more than 3,000,000 acres located close to water sources that contain chloride.It is an urgent task in China to develop these land resources to the full and make the most use of them so as to boost the country' s national economy and social progress.The currently successful approach to developing salt marshes in China is the system of elevating marshes to turn them into fish ponds.However, due to the great divergence between the water quality in salt marsh ponds and that in fresh water ponds coupled with lack of basic and theoretical research,it is no rare occasion that fish tend to die in great numbers. Even if some kinds of fish survive under marshy conditions,their growth tends to be stalled,which inevitably cuts down fish yields and causes yields to fluctuate.One of the fundamental reasons is that species of fish are not factored in according to the water quality in salt marshes. The writer of the present paper has done research on crayfish' s endurance against salinity through quick experiments.Research has also been done on the effects of varied salinity levels on crayfish fry' s growth performance indexes,oxygen consumption,and hydrogen nitride discharge as well as on the growth of crayfish zygotes.The research aims to provide a solid piece of biological proof that chloride-laden salt marshes can be regulated to farm crayfish.The research has yielded the results as follows.According to the water quality in chloride-laden salt marshes, salinity has been regulated and formulated with sea water.Under these conditions research has been carried out to gauge the effect of acute toxicity found in different salinity levels on crayfish.When the levels of salinity are at 24h,48h,72h,and 96h,the semi-mortality rates(LC50) are 30.37,26.76,25.19,and 23.93,the salinity that does not endanger crayfish is 6.23.Within salinity levels ranging from 0 to 6,all the growth performance indexes of the crayfish are good with a high survival rate, a rapid growth,and a remarkable effect of fish feed ratio that facilitates the healthy growth performance.When salinity surpasses this range and keeps rising,the fish fry' s survival rate drops.The surviving fry' s growth slows down with poor effect of fish feed ratio.Under the temperatures below 25℃and within the salinity levels ranging from 0 to 8,crayfish zygotes can hatch out.However,within salinity levels ranging from 0 to 4,zygotes hatch out at a relatively higher rate with each parent turning out a high yield of fry.When salinity rises beyond this range,zygotes hatch out at a dramatically decreased rate.With the rise of salinity,it takes zygotes a longer time to hatch out.Hence a conclusion can be drawn from these experiments that salinity levels ranging from 0 to 4 is particularly suitable for zygotes to hatch out.Within this salinity range,zygotes hatch out at a relatively high rate within a relatively short period of time.In order to minimize interference,water used in the experiments is formulated.Within the range of salinity levels set for the experiments, the rates of oxygen consumption and hydrogen nitride emission by the crayfish fry hit the lowest when the salt level is at 2.This demonstrates that the iso-osmotic of the fry in adapting to the fluctuations of salinity is around 2.With ascending salinity,the rates of oxygen consumption and hydrogen nitride emission by the crayfish fry move up accordingly.Through the Turkey HSD test,it has been discovered that the contrast group of salinity 2,4,and 6 exhibit discernible disparities in oxygen consumption and hydrogen nitride emission.
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