The blood characteristics of diploid(abbreviated 2nCC,2n=100),triploid(abbreviated 3nCC,3n=150±)and tetraploid(abbreviated 4nCC,4n=200)crucian carp coexisting in Dongting water system were studied in this research.The ploidy level was examined by flow cytometer.The nuclear traits of erythrocytes of different ploidy crucian carp(abbreviated CC)were observed.The hemoglobin contents of different ploidy CC were measured by blood analyser.The results indicated that the mean nuclear volume of erythrocytes in peripheral blood increases regularly with increasing ploidy.Moreover,some erythrocytes had dumbbell nucleus in the peripheral blood of 3nCC and 4nCC in contrast to 2nCC which resulted from amitosis.No obvious differences in hemoglobin contents were observed among different ploidy CC.Inferred from these results,amitosis that existed in erythrocytes of 3nCC and 4nCC might lead to the similar hemoglobin contents among different ploidy CC,which resulted in no obvious differences in oxygen transporting ability of blood from that of 2nCC.