The present paper deals with the fact of miniaturization of fish communityand population structures through analysing the fish catch and the characteristics of fishbiology (gut contents, growth, reproductive habits, etc.)of Carassius auratus, Cultererythropterus, Channa argus sampled from weirs and other fishing gear in Lake Gehuduring 1986-1988. The results show that the small-sized, low-value fishes in thecommunity and young fishes(younger than 1~+ group)in population take high proportions. The von Bertalanffy's growth equation and Beverton-Holt dynamic pool model areused for analysing the population dynamics of Carassius auratus. On the ecosystem ofLake Gehu fisheries, the causes of miniaturization of fish composition and correspondingcountermeasure have been discussed. An optimal age for first catch and optimal fishingintensity are suggested.