The genotoxic effects of sublethal doses of cadmium in peripheral erythrocytes of Oreochromis niloticus was investigated using micronucleus (MN) and nuclear abnormalities (NAs) tests. For this reason, the fish were exposed to medium changes of 0.5 and 1.0 mg/L doses of cadmium (Cd) during an average treatment period of 10 days. On the 2nd, 4th, 6th, and 10th days of the test period, the erythrocytes, including the micronuclei (MN) and other nuclear abnormalities such as lobbed nuclei (LB), blebbed nuclei (BL), and notched nuclei (NT), were counted and pointed out. As a positive control, a 4 mg/L dose of cyclophosphamide was used. Exposure to doses of cadmium caused significantly increased (P < 0.05) micronuclei in peripheral erythrocytes of fish. It was also observed that the application of a 1.0 mg/L dose of Cd produced more of an effect on MN frequencies than the application of a 0.5 mg/L dose. The maximum frequencies of MN were recorded on the fourth day of the experiment period. Exposure to doses of cadmium caused significantly increased (P < 0.05) NA (LB, BL, and NT) frequencies and, as with the MN results, the 1.0 mg/L dose of Cd had more of an effect than the 0.5 mg/L dose on NA frequencies. The maximum frequencies of NAs were recorded on the fourth day of the experiment. As a result of these doses of Cd, the MN and NA frequencies in peripheral erythrocytes of fish were observed to increase in relation to both the time and dose applied. However, a gradual trend of decrease was also observed starting from the sixth day.