AbstractThis study was envisaged to identify a strain of bacteria isolated from the gill of mandarin fish. Identification and characterization of the bacterial strain were performed using morphological characteristics, growth temperature, physiological and biochemical tests, antibiotic sensitivity tests, artificial infection tests, and 16S rRNA gene sequencing homology analysis. The results showed that the bacterium was Gram-negative, with flagella at the end and the side. The bacterium exhibited a light brownish-gray colony on the Luria-Bertani culture and white colony on the blood agar plate without hemolytic ring. Normal growth was achieved at 42°C, and growth could be delayed in 7% NaCl broth medium. By homology comparison and analysis, the phylogenetic tree was constructed using MEGA7.0, and the bacterium was preliminarily identified asAchromobacter. The antibiotic sensitivity test showed that the strain was sensitive to piperacillin, carbenicillin, cefoperazone, cefazolin, ofloxacin, gentamicin, kanamycin, amikacin, neomycin, erythromycin, minocycline, doxycycline, polymyxin B, tetracycline, chloramphenicol, and other drugs. However, it was resistant to penicillin, ampicillin, oxacillin, ceftriaxone, cefradine, cefalexin, cefuroxime sodium, ciprofloxacin, norfloxacin, vancomycin, compound sulfamethoxazole, clindamycin, medimycin, and furazolidone.