Introduction

It is a good opportunity that we have the honor to carry out “water-purification fishery”concept and water-purification fishery technology.

Aiming at the high concentrations of nitrogen and phosphorus in Lihu Lake even after the pollution control measures and ecological reconstruction technologies having been carried out，we used “water-purification fishery”concept whose method was water-purification fishery technologies to carry out bioremediation.

“Water-purification fishery”concept is a concept that using a type of special and appropriate fishery practice to purify eutrophication water. And its general principle is as follow：nitrogen and phosphorus in eutrophication water can be absorbed by phytoplankton，and phytoplankton can be eaten by zooplankton，and phytoplankton and zooplankton can be eaten by filter-feeding fish（silver carp and bighead carp）and zoobenthos（snail and shellfish）. Therefore，the nitrogen and phosphorus will be taken out of the eutrophication water by the way of catching fish. That is to say，the nitrogen and phosphorus could be removed and phytoplankton，including blue-green algae，could be controlled by the above food chain.

Water-purification fishery technology is different from the general practice of releasing silver carp and bighead carp into lake. Water-purification fishery technology requires releasing large-size fingerling（2 years old fingerling）and catching large-size adult fish（more than 4 years old），therefore the no catching time is very long，and what is more，a certain quantity of silver carp and bighead carp have to be left after catching. It has been well known that silver carp and bighead carp could control water bloom，however，the efficiency was not so good especially in Taihu Lake and Chaohu Lake，the crucial reasons are release，manage and catch of silver carp and bighead carp.

The research and demonstration of water-purification fishery technology and firsthand monitoring data of the research are described in this book. For the good reference purpose，we have compared with and referenced the research results of other scientists，and analyzed，researched and presented some thoughts and questions in this book. Therefore，in order to provide a model demonstration example with the combination of theoretical research and practice that using biological or ecological methods to treat lake eutrophication，the earlier stage test of eco-remediation of Lihu Lake has been described particularly. The effect of releasing filter-feeding fish on slowing down lake eutrophication and purifying water has been verified. The in situ test lasting for many years has showed that silver carp and bighead carp have the eutrophic water remediation function，however，this eutrophic water remediation function is closely related to environmental condition and operation method. This book can provide ideas for other shallow lakes in the practice of ecological restoration.

In the process of water-purification fishery research and demonstration，the authors acknowledge support from professor Zhang Xianzhong and his team from Wuxi Aquaculture Technology Extending Station for releasing，managing and catching silver carp and bighead carp that used to eutrophic water remediation. Acknowledge support from scientists from Fishery Environmental Protection Department and Large Water Hydrobiology Resources Department of Freshwater Fisheries Research Center for providing thousands of measured data about the ecological environment changes and fish stocks dynamics of Lihu Lake before and after the carrying out of water-purification fishery technology. Acknowledge support from professor Hu Gengdong for aquatic plants investigation in open water area of Lihu Lake，support from professor Yang Jian and his research team for monitoring and evaluating heavy metal pollution dynamics by the way of transplanting “standardized”Anodonta woodiana，their works have provided foundation and basis for the research.

Xu Pao et al.
October　2016