Aeromonas hydrophila is a heterotrophic, gram negative bacterium which is primary or secondary cause of ulcers, fin rot, tail rot, and hemorrhagic septicaemia in fish. The treatments for this infection are only restricted to some antibiotics. So, novel materials are being searched for combating with bacterial infections and the resulting consequences. In the present study, silver nanoparticles were synthesized chemically & biologically and characterized by UV-Visible spectrophotometer and transmission electron microscope (TEM). The antimicrobial activities of silver nanoparticles, synthesized by both the methods were checked by both well diffusion and turbidometric (spectrophotometric) method. Both biologically and chemically synthesized nanoparticles exhibited their antimicrobial efficacy in both the standard inhibitory assays; however chemically synthesized particles which were also smaller in size, exhibited more inhibitory effect than biologically synthesized nanoparticles. These results thus provide a scope for further research on the application of silver nanoparticles as disinfectant and/or antibiotic in the fishery industry.