Abstract Fish diseases caused by Pseudomonas aeruginosa, a known pathogenic organism, is responsible for considerable economic losses in the commercial cultivation of Oreochromis mossambicus (Tilapia). The bacteria were injected into healthy fish through intramuscular injection, oral and immersion challenge. Infection was confirmed by histopathological investigation of the infected organs. Lime nanoemulsion was prepared and the effectiveness of the nanoemulsion was studied both in vitro and invivo by well diffusion assay and invivo in the artificially infected fish. Results showed that the lime nanoemulsion was effective against the P. aeruginosa infection in O. mossambicus both in vitro and in vivo.