Lake anchovy, Coilia ectenes taihuensis, a kind of smallsized and zooplanktivorous fish was the dominant fish in Lake Taihu. The changes of the fish catch and the relationship with environmental variation were studied, based on historical data from 1952 to 2004 and the studies from 2003 to 2005. The results were as follow: (1) The catches of the fish increased from 640.5 t in 1952 to 21 221 t in 2004. Especially since 1994 the increase had speeded up; (2) The age structure of the fish population was that 0+ individuals occupied only 33% in 1979 and 34% in 1980, but the figure increased to 99.04% ±2.21% in 2003 and 99.08%±0.80% in 2004; (3)0+ lake anchovy mainly fed on zooplankton. Cladocera, Copepoda and Rotifera respectively accounted for 89.77%±13.69%, 7.84%±11.53% and 2.39%±4.95% of its diet. The conclusion was that, human activities such as the obstructed buildings between river and the lake, over fishing, environmental pollution and the ecological characteristics of the fishes in Lake Taihu were responsible to the changes of catches and age structures of the fish. With the fish catches increasing, there was the trend of zooplankton standing mass declining during October in the lake. So the increase of the fish catches might enhance phytoplankton development in the lake.