Exposure of Oreochromis mossambicus to sublethal levels of an organophosphorus pesticide, Ekalux, produced a time and dose dependent decrease in the Red Blood Corpuscle (RBC) count, Haemoglobin (Hb) content, and Mean Corpuscular Volume (MCV), leading to microcytic anaemia and an increase in the Total Leucocyte Count (TLC) owing to the rise in population of granulocytes. O. mossambicus exposed to 50, 100, 200, or 300 ppb Ekalux showed complete recovery in RBC count on 55, 42, 36, or 34 days and TLC on 33, 31, 37, or 42 days respectively.