Department of Animal, Aquaculture and Range Sciences

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Browsing Department of Animal, Aquaculture and Range Sciences by Subject "African catfish"

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    Identification and characterization of flavobacteriaceae from farmed Nile tilapia (Oreochromis niloticus) and African catfish (Clarius gariepinus) in Uganda
    (Sokoine University of Agriculture, 2017) Racheal, A.
    Bacteria under family Flavobacteriaceae (in this study were also referred to as Flavobacteria) are important pathogens of fish, people, many other animals and plants. In this study, Flavobacteria from Nile tilapia (Oreochromis niloticus) and African catfish (Clarius gariepinus) were identified and characterized from the selected farms in Uganda. Gill and skin swabs were obtained from a total of 119 fish from 19 farms and were dissected aseptically to sample internal organs. The samples were inoculated onto Sheih media and incubated at 25°C for 48 hours. The suspected isolates were identified by colon characteristics, conventional biochemical tests and API 20 NE kits. The isolates were grouped into eight based on colon characteristic similarity. One isolate was selected per group for 16S rRNA gene sequencing and identified using the EZbiocloud.net ID software. Phylogenetic analysis of selected isolates was performed using the 16S rRNA gene sequences in BioEdit and MEGA 7.0.2 software. Basing on extrapolation of sequence analysis of the selected isolates, out of the 86 isolates, Myroides marinus was the most predominant species taking up 4 of the 8 groups (60 isolates) in 13 farms. The rest of the groups comprised of; Acinetobacter pitti, one group (6 isolates) in 6 farms, Chryseobacterium gambrini 2 groups (3 isolates) in 3 farms and one isolate was unidentified, in 3 farms. However, a total of 16 isolates did not grow on sub culturing. Phylogenetic analysis indicated that M. marinus isolates grouped with other M. marinus isolates from gene bank with significant intra-species diversity which was also observed with C. gambrini isolates. All the sampled farms had at least one isolate of a Flavobacterium from Tilapia and/or Catfish. Pathogenicity studies should be conducted on the isolates to establish their importance as fish pathogens and transmission dynamics so that an appropriate control measure can be recommended.
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    Molecular characterization of Edwardsiella species isolated from African catfish (Clarias Gariepinus) and Nile Tilapia (Oreochromis Niloticus) in Wakiso district, Uganda
    (Sokoine University of Agriculture, 2017) Nantongo, M.
    Edwardsiella tarda is an opportunistic pathogenic bacterium that causes Edwardsiellosis in cultured and wild fish. It is among the most important bacterial diseases causing severe economic losses in fish worldwide. This study was carried out to determine the occurrence and characterize E. tarda in cultured Nile tilapia and African catfish from selected fish farms in Wakiso district, Uganda. A total of 111 fish samples were collected from 17 fish farms between September 2016 and February 2017. Clinical and post mortem examination of sampled fish was done followed by bacteriological examination of the collected internal organs (spleen, kidney and liver), gills and skin swabs. Identification of the bacterium was done using conventional biochemical tests, API 20E kits and sequencing of 16S rRNA. Phylogenetic analysis was done by Neighbor-Joining method in MEGA 7.0.2 against the 16SrRNA gene sequences retrieved from the GenBank. The isolate was screened for presence of selected virulence genes by polymerase chain reaction (PCR). From this study, one isolate from O. niloticus was identified and confirmed to be E. tarda by the 16S rRNA sequencing. The isolate gave an identity rate of 99.9% to other members of E. tarda on comparison with known 16S rRNA sequences in the GenBank database. In phylogenetic analysis, the isolate did not cluster with any of the E. tarda isolates suggesting a distant relationship with the isolates whose sequences were included in this study. Six virulence genes were detected in the isolate that enhance bacterial survival and pathogenesis in the host including; CitC, muk, gadB, katB, esaV and fimA. Although the study confirmed only one E. tarda isolate, the isolate tested positive for several virulence genes indicating their potential to cause disease in fish and since the bacterium is of public health importance, awareness should be created amongst fish farmers and stakeholders to take precaution to avoid disease outbreak.