For the sake of devising fish composition with the functions of protecting water environment,the progress of studies on the mutual relationship between fishes and water environment was analyzed and then the suggestion of devising reasonable fish community and the problems which had to be solved before devising were put forward,based on the preliminary study in Lake Taihu and the papers in the world.The contents including three parts were as follows:1.Methods of estimating fish productivity in lake fisheries and the characteristics of fish composition in most of Chinese lakes:there were totally four kinds of methods of estimating fish productivity such as regression analysis methods based on regression statistics,energy methods based on food and inverted efficiency of energy,integrated analogy methods and systemic evaluated methods.The characteristics of fish composition in most of Chinese lakes was that the dominant fish species were phytoplanktivores,zooplanktivores and omnivores fishes usually with short food chain and that little-sized fishes increased because of controlling of piscivores,over fishing,the obstructed between river and lake and environmental deterioration.2.The top-down effects of fishes on environment:the developed countries played much more attention to the study and the practice of the top-down effects of fishes on environment.Changing fish composition was one of the important ways to carry out restoration and rebuilding of ecosystem to deal with eutrophication.For instance,the traditional biomanipulation which Shapiro put and the non-traditional biomanipulation which Xie put were such ways.It was the main mechanism of the traditional biomanipulation that large-sized zooplankton were protected and developed by adjusting the structure and composition of fish fauna.The main mechanism of the non-traditional biomanipulation was that restocking fishes such as bighead and silver carp directly fed on cyanobacteria bloom.The fish composition in most of Chinese lakes with the characteristics of short food chain helped to sharpen the degree of eutrophication and reduce diversities of ecosystem.Chinese researches had studied the effects of grass carp on ecosystem and vegetation,the effects of bighead and silver carp on the structures and functions in micro-ecosystem,and the effects of Chinese carp and crucial carp on the recycling of N and P.The course of the aggravation of eutrophication in Chinese lakes was considered to be consistent with the development of lake fisheries in which “four fishes” such as bighead,silver carp,grass and black carp were mainly cultured.3.Devising reasonable fish composition with the functions of protecting water environment and the problems which had to be solved before devising:reasonable fish community should had such functions as protecting zooplankton,protecting vegetation,protecting zoobenthos and not disturbing bottom mud.If fish composition with the functions of protecting water environment was to be designed,these problems should be solved:the changes of fish composition corresponding to environmental change,the changes of diet composition of main fishes,the efficiencies of fish assimilating and absorbing cyanobacteria bloom and the estimating of fish productivity under conditions of eutrophication,the quantificational index and methods of analyzing fish diet composition which could be compared,the quantificational model of fish population changes which could express the mutual effects among fish population.
