Abstract: By means of population accumulative culture and with a green algae Chlorella pyrenoidosa at four food levels (3.0×106,6.0×106,9.0×106 and 12.0×106 cells/mL),the effects of food concentration on the body and egg volume,and population growth in freshwater rotifers Brachionus angularis were studied at (25±1) ℃.The rotifers belong to Guangzhou,Wuhu and Yingshang strains collected from the water systems of Zhujiang River,Changjiang River and Huaihe River respectively.The results showed that the body and egg volume,and population growth were affected significantly by food concentration,strain and the interaction of both.At the same food level,the rotifer of Guangzhou strain had the largest population growth rate,and that of Wuhu strain had the largest body volume and egg volume.At the same strain,the population grew fastest while the food concentration was 9.0×106 cells/mL.The relationships between the food concentration and population growth rate were all curvilinear in three strains.However,the optimum food concentration for the population growth was different among them.The strain had a more important effect on the rotifer body volume than the food concentration did.