An extensive array of fish microbes has the likelihood of causing diseases, which make them one of the most paramount concerns in fish farming sector. An aquaculture farm in Narok County, Kenya reported mass mortality of its reared fish from unknown aetiology in May 2022. The fish farm stocks Nile tilapia, catfish and ornamental fish. The objective of this study was to establish antimicrobial susceptibility of Aeromonas veronii biovar sobria (A4 strain) isolate recovered from this farm. Following Clinical Laboratory Standards Institute protocols, the Aeromonas veronii biovar sobria (A4 strain) was screened for resistance against 19 antimicrobials using Kirby Bauer disc-diffusion method. The bacterium was resistant to ceftazidime, imipenem and meropenem. However, it was sensitive to the rest of the antimicrobials used in the study. The bacterium was associated with marked resistance to some antimicrobials. The findings indicate a need for more studies on this bacterium’s pathogenicity and development of a vaccine. Further, enhanced biosecurity is required for its prevention and control.