The present study targeted the evaluation of Spirulina spp. (Sp) and Nannochloropsis genus (Nano) as a partial substitution of soybeans on general health of O. niloticus through haematological analysis and histological study by seven treatments as follow: negative control (T1), three levels of Spirulina spp. (Sp) 3 % Sp (T2), 5 % Sp (T3) and 7 % Sp (T4), three levels of Nannochloropsis genus (Nano) as follow: 3 % Nano (T5), 5 % Nano (T6) and 7 % Nano (T7). Results indicated that T6 had higher significant (P < 0.05) final body weight (FBW), average weight gain (AWG), specific growth rate (SGR) and relative growth rate (RGR) compared with the other experimental treatments. However, the best feed conversion ratio (FCR), was found in T7. No mortality was observed in T4 and T7. The RBCs count was in favor of T4 and T3, and the leucocytes count T5 and T6 respectively versus the control. The hemoglobin concentration related parameters (Hb, HCT and MCV) showed the highest significant values (P