Molecular-Biochemical Identification and Antibiotic Sensitivity of Pathogenic Bacteria Isolated from Diseased Gangetic Mystus (Mystus cavasius, Hamilton 1822) in Biofloc Aquaculture

Biofloc technology has shown more production compared to the conventional fish culture but disease outbreaks have been seen to impede productivity. To identify pathogenic bacteria from diseased Gangetic Mystus (Mystus cavasius), using molecular, and biochemical techniques and to find out effective antibiotics. Bacterial samples from diseased fishes were cultured on nutrient agar and Rimler-Shotts (R-S) media. Various Biochemical tests like Gram’s Staining, Triple Sugar Iron test, Catalase test, Motility test, Carbohydrate Fermentation test, Indole test, Methylred and Voges-Proskaur (MR-VP) test were performed. Sensitivity of isolated bacteria was tested against 15 commercially available antibiotics. Colony Characteristics from both nutrient agar and R-S media and the results of biochemical tests indicated that the suspected pathogens were Aeromonas spp. The obtained 16S rRNA gene sequence (1410 bp) from M. cavasius confirmed that the isolated bacteria was Aeromonas veronii which showed 99.93% similarity with the complete genome of A. veronii (GenBank Accession number CP034967.1). Distinct clinical sings in the gill, kidney, spleen, and skin of M. cavasius were reliable indicators of bacterial pathogenicity. Among tested 15 antibiotics Streptomycin, Ciprofloxacin and Gentamycin were found more effective against A. veronii. The findings of this research will be helpful to identify specific bacteria and to control bacterial diseases of M. cavasius.