Abstract:
Pathogenic microorganisms associated with the African Nile Tilapia (Oreochromis niloticus) in Old and New Owena Reservoirs were investigated for their ability to serve as a pollution indicator in the reservoirs. Two hundred and fifty (240) samples of Oreochromis niloticus with a mean body weight of 107.87g and 104.16g were collected from the Old and New Owena Reservoirs respectively. These were randomly and bi-monthly sampled from February to April, 2016 and analysed for their morphometric and microbiological examinations. Samples of water and sediments from the reservoirs were also examined for their microbiological and physico-chemical properties. Sections of the fish gut were aseptically removed by means of sterile scalpel and pair of sterile scissors. About five (5g) of the sections were homogenized in 6ml of sterile distilled water which served as the original stock solution. The associated microbial isolates were counted by standard microbiological methods. Isolates that were confirmed as human pathogens were subjected to an anti-biotic sensitivity test using the single disc diffusion method while the three most prevalent microbes from the pure culture of isolated microbes were employed for an invitro-pathogenic test. Study on the Length-weight relationship and Condition factor of O. niloticus from the Old and New Owena Reservoirs showed a strong correlation between the length and weight of the fish from both reservoirs. Values of the physico-chemical parameters of the two reservoirs were within the permissible ranges for warm water fish. Water temperature recorded was also less than the 35˚C specification of the Federal Environmental Protection Agency.
A total of 66 bacterial species and 33fungal species were isolated from Old Owena Reservoir while 53 bacterial and 28 fungal species were isolated from the New Owena Reservoir. The frequency of occurrence of the isolated bacteria indicated that E. coli had the highest (16.67%) occurrence frequency while Pseudomonas aeruginosa recorded the least (7.58%) occurrence frequency in Old Owena Reservoir. In the new Owena Reservoir, highest (16.98%) and lowest (7.55%) occurrence frequencies were recorded for Ecoli and Pseudomonas aeruginosa respectively. Penicilum italicum and Trichoderma sp recorded the highest (32.14%) and the least (7.14%) fungal occurrence frequency in New Owena Reservoir while the most occurred fungi in old Owena reservoir was Penicilium italicum 9(27.27%). The highest mortality rate (96.67%) was observed at 30.0ml inoculum of E. coli, Shigella sp. and Salmonella sp. combinations. The results from this study indicated that both water and fish samples from the reservoirs were less contaminated with pathogenic bacteria since all the values were found to be markedly lower than the acceptable limit of 106/g (ICMF, 2008
