This study investigated the bacteria present in natural and cultured fish species from the same aquatic system, and difference of their antibiotic resistance. A total of 129 fish, Georgian shemaya (Alburnus derjugini), black sea salmon (Salmo labrax) and rainbow trout (Oncorhynchus mykiss), were sampled on a monthly basis between the months of October 2016 and September 2017 in Kürtün Dam Lake. A total of 41 bacterial isolates were isolated from the fishes. The bacterial species were identified

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... by molecular methods (PCR) using universal primers for bacteria. Acinetobacter lwoffii, Acinetobacter sp., Aeromonas sobria, and Pseudomonas sp. were isolated from both wild and cultured fish. Yersinia ruckeri was isolated from cultured fish, which showed severe mortality rate and typical symptoms. Various antibiotics including ampicillin (AMP10µg), gentamicin (CN10 µg), oxytetracycline (T30 µg), amoxicillin/clavulanic acid (AMC10µg), enrofloxacin (ENR5µg), trimethoprim/sulfamethoxazol (TMP-SMZ25µg), florfenicol (FFC30µg), sulfamethoxazol (SMZ25µg) and erythromycin (E15µg) were used for determination of the bacterial resistances. The highest resistances were determined against ampicillin (56%), sulfamethoxazol (46.3%) and oxytetracycline (34.1) in all bacterial isolates. While the bacteria isolated from wild fish did not show resistance to enrofloxacin and amoxicillin/clavulanic acid, those from cultured fish did not show resistance to gentamicin and erythromycin.