ISOLATION, IDENTIFICATION AND ANTIBIOGRAM PROFILE OF BACTERIA ISOLATED FROM VIETNAMESE KOI (Anabas testudineus) OF SELECTED OUTBREAK AREAS IN MYMENSINGH DISTRICT

Abstract

Vietnamese Koi (Anabas testudineus) is considered as a high value fish species in Bangladesh. The fish contains high amount of iron and copper, which are nutritionally beneficial for hemoglobin synthesis in human. A total number of hundred seventy five of infected /dead V. Koi fishes were collected during outbreak period from seven different areas in Mymensingh district for conducting this study. The main purpose of this study was to isolate and identify the bacterial spp. responsible for mass mortality of V. Koi from selected outbreak areas in Mymensingh district and to know the pathogenicity of the isolated bacteria. The main clinical symptoms were hemorrhage in base of the fin, slight lesion on body, body and tail erosion. Post-mortem changes indicated congestion and enlargement with hemorrhage in liver, kidney and spleen .Isolation and identification of bacteria was conducted by studying cultural properties, gram staining and biochemical properties. Biochemical tests for bacteria which were performed by API kit indicated positive results by reacting with betagalactosidase, arginine dihydrolase, lysine decarboxylase, sodium citrate, tryptophan deaminase, sodium pyruvate, gelatinase, glucose, mannitol, sucrose, melibiose, amygdalin, and arabinose for all isolates. And showed negative result when tested for ornithine decarboxylase, H2S production, inositol, sorbitol, and rhamnose. Among the various isolated bacteria, Aeromonas hydrophila and A. caviae were appeared as main pathogen in the infected fishes. Total bacterial load found at 1.13×106 to 3.21×108 cfu/g in lesions; 1.10×105 to 2.1×107 cfu/g in liver; 3.24× 04 to 3.82×106 cfu/g in gill; 1.25×106 to 3.51×107 cfu/g in kidney and 3.74×104 to 2.43×106 in spleen of diseased Koi. Cumulative mortality rate was recorded the highest (89%) at the group 2 after 14 days of post inoculation because of the infection of Aeromonas hydrophila. Commercially available antibiotics were used for the determination of sensitivity test for the isolated bacteria. All the isolated bacteria were found sensitive to endrofloxacin, ciprofloxacine, levofloxacine, azithromycin and gentamicin. Ciprofloxacine and levofloxacine were highly effective against A. hydrophila and A. caviae. Ampicillin & penicillin did not show any activity against Aeromonas spp. Study indicated that motile Aeromonas sp. perhaps serve as the primary cause of hemorrhages, ulcerations and skin lesions as well as mortality of V. Koi. The result of this study will be useful for V. Koi aquaculture by applying right antibiotics against Aeromonas spp. in order to prevent mass mortality.