Abstract: Bacterial pathogens are major threat to the aquaculture industry and small scale aqua farming. The emergence of various virulence pathogens during the culturing period leads to mass mortality and influence the loss of aquaculture production. As a result it causes economic imbalance. This relies on the very importance position to serve the protein rich sources for human consumption. In order to improve the sustainable aquaculture production the biologically synthesized silver nanoparticles have been used as an alternative method for commercial antibiotics to control such pathogenic infection. Marine microalgae Caulerpa racemosa was used as a silver reducing agent in this study. This controls Pseudomonas aeruginosa infection in tilapia. The bioactive compounds present in the extracts showed potential antioxidant and antibacterial activities against P. aeruginosa infection. The formation of AgNPs was observed by the visualization of the colour change and further confirmed by the UV spectroscopy. It was characterised by Dynamic light scattering measurements (DLS). The antibacterial activity was tested against the fish pathogen. It was found to be effective.