Abstract:

The four Chinese farmed carps,i.e.black carp,grass carp,silver carp and bighead carp are economically important species in the Yangtze River.In the recent two or three decades,the resource abundance of these fish has abruptly declined.There are many influenced factors,in which the largescale water control project constructing is one of the most important reasons.In order to conserve these four species and provide the basis for ecological operation of largescale water control project,nine ecohydrological indicators in the middle reach of the Yangtze River,including the flow rise number,total flow rise days,starting stream flow,increasing rate of stream flow,continuous period of rising of water level in a flood period,et al. have been used and quantitative analyzed during the breeding season.It was found,there were no significant differences between the spawning grounds and common reaches for the nine indicators.It means that the selected indicators are only the necessary conditions for the four freshwater fishes spawning,but not the whole influencing elements.After Three Gorges Project began to run in 2003,most of the selected ecohydrological indices have no significant changes in the breeding season in Jiangkou typical spawning ground section,but the increasing rate of water level has been reduced slightly in the same section.Due to the time series data after Three Gorges Project storing water were short and the water situations of the 2004～2006 year were special,it was still unable to quantitatively analyze the influence of the four fish spawning grounds by the Three Gorges Project construction.

Key words: ecohydrological index, ecohydrological characteristic, the middle reach of the Yangtze River, the four famous freshwater fishes, spawning ground