Recently, researchers in aquaculture become interested in green synthesized nanomaterials as a superior alternative to current conventional methodologies. The present work shows that Moringa oleifera synthesized magnetite nanoparticles (MS-Fe3O4NPs) might offer a possible substitute for common antibiotics to treat Aeromonas sobria infection in African catfish (Clarias gariepinus). MS-Fe3O4NPs demonstrated an in vitro antibacterial potential (21 mm inhibition zone) against A. sobria. The fish (n = 120; average body weight: 90 ± 3.5 g) were randomized into four groups (control, MS-Fe3O4NPs, A. sobria, and MS-Fe3O4NPs + A. sobria), where 1.2 mg/L of MS-Fe3O4NPs was used as bath treatment for seven-days. A. sobria infection caused substantial elevations in malondialdehyde, tumor necrosis factor-alpha, stress indices, and hepato-renal biomarkers as well as a lower survival rate. Moreover, an apparent depletion in the level of antioxidants, the protein profile, and immune indicators were the consequences of A. sobria infection. Surprisingly, treatment of A. sobria-infected fish with MSFe3O4NPs recovered these parameters. Hence, MS-Fe3O4NPs as a water additive show promise as an antibacterial treatment against A. sobria in fish.