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¹ Al-Farabi Kazakh National University, Faculty of Biology and Biotechnology, Department of Zoology, Histology and Cytology, Almaty, Kazakhstan.
² Republic of Türkiye Ministry of Agriculture and Forestry General Directorate of Agricultural Research And Policies, Central Fisheries Research Institute, Department of Fish Health, Trabzon, Türkiye, 61250. DOI : 10.4194/AQUAST3567 Viewed : 156 - Downloaded : 174 Despite the rapid expansion of aquaculture in Central Asia, information regarding bacterial pathogens and antimicrobial resistance in trout farming systems remains limited. The present study investigated the occurrence of bacterial pathogens, antimicrobial susceptibility patterns, and antibiotic resistance genes (ARGs) in rainbow trout cultured in major aquaculture systems of the Almaty region, Kazakhstan, including flow-through, hatchery, and recirculating aquaculture systems (RAS). A total of 120 fish exhibiting clinical signs of infection were collected during the summer and winter seasons of 2024. Bacterial identification was performed using conventional microbiological methods and partial 16S rRNA gene sequencing. Bacterial growth was detected in 116 of the examined fish samples, indicating a high prevalence of bacterial agents in the investigated aquaculture systems. Sequence analysis of partial 16S rRNA genes identified 11 bacterial isolates representing four taxa, predominantly Aeromonas spp. Species of the genera Aeromonas, Yersinia, Pseudomonas, and Acinetobacter were detected in the flow-through system. In contrast, only Aeromonas and Yersinia species were identified in the hatchery, while the RAS system exclusively harbored Aeromonas species. A clear seasonal trend was observed, with all of the isolates recovered during the summer season. Antimicrobial susceptibility testing revealed high resistance rates to lincomycin (100%), amoxicillin (80%), and penicillin (70%), whereas all isolates were susceptible to florfenicol. The multiple antibiotic resistance (MAR) index ranged from 0.37 to 0.87. Molecular screening demonstrated a high prevalence of β-lactam resistance genes, particularly ampC and blaTEM. To the best of our knowledge, this study represents the first systematic investigation of bacterial pathogens and associated antimicrobial resistance in rainbow trout aquaculture systems in Kazakhstan. These findings provide important insights into the seasonal distribution and resistance characteristics of bacterial agents and highlight the need for continuous surveillance and prudent antimicrobial use in aquaculture production systems. Keywords : Kazakhstan aquaculture Rainbow trout Antimicrobial resistance Antimicrobial resistance genes MAR index