Abstract: An Investigation was made on the biology of the P.pekinensis,a semi-migratory fish bet- ween rivers and lakes,from Nov.1983 to Dec.1985 in Lake Qingling,which is linked with the main stream of the Yangtze River by a canal.The results are summerized as follows: (1)The “fry check” and “spawning check” were clearly obverved on the scales. (2)The fish reached a mean body length of 83 mm in the first year,164 mm in the se- cond year and 260 mm in the third year.The weight gain by adult females is much greater than that by adult males. (3)Over 10 vegetable food species were found in the intestine of the fish.The main spe-cies were Myriophyllum spicatum,Hydrilla verticillata and Spirogyra sp.The fish hardly ate Potamogeton crispus and Ceratophyllum demersum,which spread seasonally all over the lake,showing the habits of selective feeding. (4)During the spawning season,most mature fish were hindered from migrating into the river to spawn by the sluice gate between the river and lake.However,the tempo- rary flowing water caused by heavy rains and overflow near the inlet or outlet of the lake could still stimulate the parent fish to spawn in the lake.Owing to lack of the condition of constant flowing water in the lake,the drifting eggs then sank onto the bottom and died. (5)The population in the lake is recruited by the young fish from the river.These young individuals frequently aggregate outside the gate and may occasionally swim into the lake during the temporary lifting of the sluice gate.