Fish have high flexibility to live in diverse environmental conditions, since it have vast capability to be adjusted in adverse conditions. Such adjustments include increase of RBCs count, hematocrit (Hct) ratio and hemoglobin (Hb) concentrations, since blood is a perfect mirror apparently reflects health status of the fish. In the present studies, the blood picture of Nile tilapia reared in ponds of four different fish farms; (A) of Central Laboratory for Aquaculture Research (CLAR), supplied mostly with under-groundwater, (B) private fish farm supplied with agricultural drainage water, (C) of World Fish Center (WFC) irrigated with fresh water from Ismailia canal and (D) private fish farm supplied with sewage water from Bahr El-Baqar drain. It was found that, the erythrocyte's count of fish raised in fish farm (C) of WFC is the highest (1.859±0.091 10⁶/µl) at summer in between other investigated fish farms. The same trend was also shown for haematocrit (Hct) %, its highest value (22.765 ± 0.813%) was recorded in tilapia of farm (C) at summer. These may be attributed to the adverse ecological parameters that influence on health status of the fish like dissolved O₂, pH, temperature and chemical pollutants present in the other fish farms. On the contrary, the haemoglobin (Hb) content showed its highest value (8.99±0.743g/dl) in fish of fish farm (D) supplies with water from Bahr El-Baqar drain, at spring. Regarding to the erythrocyte indices; mean cell volume (MCV), mean cell haemoglobin (MCH) and mean cell haemoglobin concentration (MCHC) were varied in fish of the investigated fish farms. Their highest values (162.539±8.508 µ3, 69.790±6.212 Pg and 43.420±3.736 g/dl, respectively) were documented in fish farm (D) at autumn. These haematological indices are critical and serving as indicators of anemia. Nonetheless, the lowest values of these indices (128.247±5.860 µ³, 36.835±2.620 Pg and 28.449±1.277 g/dl, respectively) were confirmed in fish farm (C) especially at winter, displaying almost healthy fish status.