Abstract 

Bacterial diseases in fish are becoming increasingly significant as they pose a serious threat to aquaculture species. Among these, infections caused by Pseudomonas are particularly notable due mass mortalities in farmed fish. A study on the species composition and population density of the bacterium Pseudomonas in Nile tilapia (Oreochromis niloticus) from aquaculture ponds in Ethiopia’s Central and Rift Valley region. The internal tissues, liver, spleen, kidney, and muscle were used for screening using the   Pseudomonas Base Agar with CetriNix Supplement (FD029), alongside morphological and biochemical tests, and MALDI-TOF. Antibiotic susceptibility was determined using the Kirby-Bauer disc diffusion method. The findings revealed that P. fluorescens was the most prevalent species (49.38%), followed by P. putida (39.50%) and P. aeruginosa (11.11%) (P > 0.001). The Antibiogram analysis showed that Pseudomonas spp. were sensitive to Ceftriaxone, Gentamicin, and Ciprofloxacin but resistant to Amoxicillin-clavulanate, Ampicillin, and Erythromycin. High susceptibility was observed to ceftriaxone, gentamicin, ciprofloxacin, and streptomycin, whereas universal resistance was detected to amoxicillin-clavulanate, ampicillin, and erythromycin. Infection prevalence was significantly higher in males than in females and varied among organs and study locations, with the highest prevalence recorded in Ziway.  This study demonstrates the role of Pseudomonas spp. as major pathogens in Ethiopian aquaculture, highlights trends in antimicrobial resistance, and provides baseline data for disease management.

Keywords: Antibiogram, Nile tilapia, prevalence Pseudomonas, Aquaculture