1916 specimens in total were sampled from April, 1987 to March, 1988 for the investigation of the age, growth, reproduction and feeding of C. erythropterus in Honghu Lake, a heavily weeded large shallow lake with 35,500 hectares in area, and the diminution phenomenon of fish species, namely, the dominancy of small-sized species in the catch, was preliminarily studied. The results are as follows: 1. The age can be determined on the scales; the annuli can be identified by the presence of "check" or by the transition from loosely-spaced circuli to the densely-spaced ones. The formation time of annuli is from late April to July. The main component in the catch of Culter erythropterus was 2-year-old fish, while the eldest was 5-year-old for female, and 4-year-old for male. 2. The growth rate was very slow and a inflexion in 3-year-old. The body length growth curve is a smoothly convex and gradually gets to its asymptote. L_α 32.05 cm in female, and 24.18 cm in male. The body weight growth curve is sigmoid and has a inflection when t = 3.4 year. The asymptotical weight is 414.908. So 3-year-old is the theoretical age of catching. 3. A few individuals could attain sexual maturity in the second year after hatching, but all matured in the third year. The fecondity changed in the range of 2.473--80.243 eggs, and varied with body length as well as age. The eggs matured to be laid in batches, (most in two batches). Breeding season is from May to early August. 4. The diet is listed. The main foods ingested were small fishes shrimps and rapidly digested in the fore part of the gut. The feeding frequency is low and the changes of feeding season is not apparent. 5. The diminution phenomenon is indicated by the sharp increase of small-sized fishes in the composition of the catch as a result of the decrease in the quantities of big-sized fishes because of environmental changes and over-fishing. The environmental alterations, such as obstruction of the passage between the river and the lake, great increments of aquatic plants, resulted in the extinction of migratory fishes in one hand and in another the decrease of big-sized, lake-inhabiting fishes for the difficulty in adaptation. Over-fishing may destroy the reproduction of big-sized fishes populations. These two aspects would decease the recruitments of big-sized fishes and increase the quantities of small-sized fish as result of evolvment of fishes community hierarchy.