author(s)
Ashaduzzaman, Rezina Laz and Biswanath Sikdar

abstract
The present study was conducted on diseased fish, Labeo rohita collected from in Rajshahi city corporation area. Bacterial isolates, BSLR₁, BSLR₂ and BSLR₃ were identified. The isolates showed round/spherical shape with pale yellow and yellowish pigmentation. All bacterial isolates were gram positive and showed negative reactions in oxidase, potassium hydroxide, Simmon citrate, MacConkey, methyl red and urease tests as well as positive reactions in catalase test. BSLR₃ showed positive in triple sugar iron test while BSLR₁ and BSLR₂ were negative. BSLR₂ were positive in sulphur indole motility test but BSLR₁ and BSLR₃ showed negative. BSLR₂ and BSLR₃ exhibited positive reactions in kligler iron test but BSLR₁ was negative. Antibiotic sensitivity test was performed in this study. All bacterial isolates showed sensitivity to Erythromycin, Azithromycin, Gentamycin and resistant as well as intermediate to Oxytetracycline and Neomycin respectively. In case of Doxycycline, BSLR₁ showed intermediate but BSLR₂ and BSLR₃ were sensitive. BSLR₃ showed intermediate to cefotaxime but others exhibited sensitive. BSLR₁ showed intermediate to Sulfonamide whereas others were sensitive. Three strains of Staphylococcus aureus was confirmed by Molecular identification. In aartificial infestation, all isolates showed no infestation at 100µl suspensions but at 300µl, infestations were found in all fish aquaria. All isolates showed both infestation and non-infestation at 200µl suspensions.