Isoltion And Identificationof Aerobic Bacteria Of Gills And Intestines Of Orechromis Niloticusfish Raised In Alshagara Fish Farm

This study was carried out in Alshagara fish farm, Alshagara Fisheries Research Station, 11 Km south of Khartoum on the eastern bank of White Nile, to isolate and identify the aerobic bacteria associatedwith gills and intestines of apparently healthy Oreochromis niloticus. Sixty gill and 60 upper part of intestine samples of apparently healthy O. niloticusof different sizes 200 g -300 g and lengths 17 cm – 23 cm were aseptically collected in sterile containers from nursery earthen ponds (20 x 50 m 2 with depth 1 m) in Alshagara fish farm during the autumn season. Ponds water supply directly from WhiteNile River. Ponds water was daily examined through the measurement ofpH, temperature and oxygen content of water in the ponds. Gill and intestine samples were inoculated onto blood agar and MacConkey agar media and incubated overnight at 37° C for isolation of aerobic bacteria. The purified isolates were identified according to Gram staining reaction, cell morphology, cultural characteristics, and biochemical characteristics. The sensitivity of bacteria isolated from apparently healthy O.niloticusto the following antibiotics Ampicillin/Sulbactam, Co-Trimoxazole, Cefotaxime, Chloramphenicol, Ciprofloxacin, Ceftizoxime, Tetracycline, Ofloxacin, Gentamycin and Pefloxacin was performed. All collected samples showed bacterial growth and yielded 167 isolates. One hundred and thirty seven (82.04%) of isolates were found to be Gram-negative bacteria and the remaining 30 (17.96%) isolates were Gram positive bacteria. The Gram-negative bacteria isolated were 30 (25%) Aeromonas hydrophila, 11 (9.17%) Aeromonas sobria, 9 (7.5%) 10 Pseudomonas aeruginosa, 21 (17.5%)Citrobacter freundii, 16 (13.33%) Escherichia coli, 16 (13.33%)Enterobacter aerogenesand 34 (28.33%) Enterobacter cloacae. The Gram-positive bacteriaisolated were 18 (15%) Bacillus macerans, 2 (1.67%) Micrococcus varians, 9 (7.5%) Staphylococcus gallinarumand 1 (0.83%)Enterococcus casseliflavus. The result of sensitivity test was variable. Most species of bacteria isolated were sensitive to gentamycin (95.45%), chloramphenicol (92.73%), ciprofloxacin (91.82%) and Cefotaxime (90.91%) but highly resistant to Ampicillin/Sulbactam (50%). Pseudomonas aeruginosaand Enterococcus casseliflavuswere resistant to ampicillin/sulbactam, ceftizoxime, tetracycline, ofloxacin and pefloxacin. In this study the aerobic bacteria of O. niloticusin Alshagara fish farm were identified. Some of these bacteriamay cause bacterial diseases in fish farm if the environmental conditions in the farm are altered or fish’s resistance is reduced