Hematological analyses were used as biomarkers in Oreochromis niloticus from polluted pond and fishfarm (negative control) in winter, spring and summer. Water column from polluted pond were also taken from acute toxicity to Daphnia similis. The pond waters were toxic in spring and winter to D. similis, but this toxicity was not detected in summer, also presented higher values of hardness, conductivity and ammonia. In fish was evaluated total leukocytes (TLC), trombocytes (TT) and differential leukocytes (neutrophyls, basophils, eosinophils, lymphocytes and monocytes). The fish collected at pond exhibited increased in percentages of trombocytes, immature erythrocytes, lymphocytes and monocytes. Total leucocytes and neutrophyls differed significantly between pond and control.