Abstract: Based on the data obtained by monthly samplings from Fuxian Lake in the duration of one year (Nov.1988 to Nov.1989),the author has investigated into the biological characters of fishes of Fuxian Lake.From the viewpoint that organisms evolve along with their environments,the adaptative significance of these characters are further explained with reference to the geological history of Fuxian Lake.It is found that a series of common characters are shared by all or many species of fishes.These common characters can be further recognized as original or derived ones according to the principle of character analysis.The original characters suggest that the extant fishes of Fuxian Lake be originated from the ichthyofauna of rivers connected to the lake.The derived characters are supposed to be evolved from adaptations of the fishes to the deepening and oligotrophic development of the lake.According to the data in living spaces,the adults of all species can be divided into three types,they are:coastal dwellers,offshore mid-upper dwellers and offshore mid-lower dwellers.However,the larvae of all species live together in coastal zone of the lake.Differentiations in adults living spaces should be a derived characters and represent their adaptation to the deepening and oligotrophic development of the lake.The habits of larvae in living spaces should be an original characters and suggest that the ancestors of extant fishes be hill-stream dwellers.This differentiation in living spaces can be shown as Fig.1.When comparing to their congeners,most fishes share a slower growth rate,a more slender body and a small body size (Table 1,2,3,4,5).The oligotrophic development of the lake must have lead food shortage to the fishes.It was the increasing food shortage that had caused the fishes to grow more slowly and to form a smaller body size.The fishes of the lake are characterized by having long spawning seasons and the existence of a regular interval between the spawning activities of any two breeding populations.These breeding habits can ensure that the limited spawning sites would be fully used and that the limited food resources would be effectively used by the larvae.Some species of fishes have relatively lower individual fecundities than their congeners.This is closely related to the oligotrophic development of the lake.Increasing food shortage can usually cause fishes to have lower individual fecundities.The sexual ratios of most species show great disparity and the females are usually dominant in a population (Table 6).It is those differentiations mentioned above that have resulted in the diverse extant fishes of Fuxian Lake.