The Effects Of Several Chinese Common Fish On Traditional Biomanipulation

Eutrophication has become the main problems affecting the lake water quality all around the world. Studies in Europe and the United States have shown that traditional biomanipulation is an effective method dealing with eutrophic lakes and water governance, and many successful traditional biomanipulation exercises have been conducted internationally, but in China the case is less successful. Because a lot of lakes in China are breeding economical fish which is a restricting factor of the implementation of traditional biomanipulation.This paper studied common fish's effect on traditional biomanipulation in the shallow lakes with eutrophication in China, which has an important significance for dealing with eutrophic lakes by means of traditional bio-manipulation.The experiments were conducted in21experimental enclosures in East Lake. The experiment time was three months from August2011to October. The experiment chose one enclosure only with large Cladocera Daphnia (100ind./L) as control group, the other enclosures were not only with large Cladocera Daphnia but also with fish from the middle and lower reach of the Yangtze River (each amount is50g/m3). The density of Daphnia magna in enclosures with silver carp decreased to the minimum; in bighead carp, common carp and crucian carp enclosures, Daphnia magna survival are greatly reduced compared with the control. Meanwhile, the density of cyanobacteria and green algae in silver carp enclosure is lower than the control group, the density of cyanobacteria in carp and crucian carp enclosures increased significantly. Physical and chemical indicators of water bodies within each enclosure changed differently under the influence of different fish and plankton density. Silver carp enclosure has higher water transparency than others. In the common carp and crucian carp enclosures, the content of water's TP, TN and chlorophyll a also rise. Accordingly, the appropriate density of silver carp have a certain role in promoting traditional biomanipulation while breeding common carp and crucian carp is not conducive to traditional biomanipulation.This experiment has studied the effect of silver carp in the low and high nitrogen levels on the classical biological manipulation.The results showed that the different total nitrogen nutritional level has different effects on traditional biomanipulation. Low nitrogen levels (TP=50μg/L, TN≤1.5mg/L) contrast of high nitrogen levels (TP=50μg/L, TN≤3mg/L) in the higher degree of transparency, total phosphorus, potassium permanganate index and chlorophyll content were lower, and the density of cyanobacteria and green algae also significantly lower. This reveals the density of silver carp in the lower level of total nitrogen play a positive role in promoting traditional biomanipulation.The indoor experiment of different fish feeding on Daphnia magna at different temperatures shows the most average daily feeding of Daphnia magna is by crucian carp, followed by bighead carp, at least by silver carp at three different temperatures. At30℃, the volume of a variety of fish feeding on Daphnia magna is the highest, followed by25℃.In summary, it is useful to carry out classical biological manipulation for controlling lake eutrophication in appropriate fish lakes of the appropriate density.