This study was conducted on 150 (one hundred and fifty) Clarias gariepinus to investigate the blood lipids (triglycerides and cholesterol), kidney functions (creatinine and urea), liver functions (ALT – AST - ALP - LDH), antioxidants (CAT – SOD - GPx) and growth performance (body weight and weight gain). The study was designed by dividing the fish into 3 groups: Group 1: (Control Group), Group 2: (2.4 mg manganese oxide nanoparticles/kg ration) and Group 3 (1.2 mg manganese oxide nanoparticles/kg ration). Samples were collected on day 15, 30, 45 and 60 of the experiment and blood samples were collected for serum separation. The results of this study indicated that the 2^nd group exhibited a significant and progressive decrease in triglycerides, cholesterol, ALT, AST, ALP, LDH, creatinine and urea at all experiment times compared to the control group.  Shifting to the antioxidants, the 2^nd and 3^rd groups showed a significant increase in CAT, SOD and GPx levels in the serum compared with the control group at day 60 of the experiment. Concerning the results of growth performance, both groups reflected a significant improvement in body weight and weight gain compared with the control group.