Abstract: The composit ion of fish communi ties showed that the migr ation fish species between river and lake was disappeared in the main area of Taihu Lake , except the stocked species .The main dominant species wer e lake anchovy (Coil ia ectenes), Icefishes and smaller Cypr inids .The coef ficient of associat ion be tween 8 dominant species showed that lake anchovy , Icefishes , Palaemon modestus , Toxabramis swinhonis , and Neosalanx ol igodont is have a similar temporal and spa tial dist ribut ions , and similar prey , but the y have diff erent reproduct ion per iod .Generally , loss or r eduction of a pr eda tor will lower the pr edation mor tali ty of its prey , causing an incr ease of prey densi ty and a concomitant incr ease in interspecific compet ition .