PhD Theses

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Browsing PhD Theses by Author "Shayo, Salome Daniel"

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    Epizootiology of microbial diseases of wild and cultured fish in the Mtera dam catchment area, Tanzania
    (University of Dar es Salaam, 2015) Shayo, Salome Daniel
    Bacterial diseases are responsible for heavy mortalities of fish in wild environment and cultured systems worldwide, thus causing significant economic losses threatening livelihood of people. In the present study, causes of outbreak of ulcerative infections and mortalities in Nile tilapia (Oreochromis niloticus) at Mtera dam and in fish farms around the Mtera catchment were investigated. Collections of fish samples for examination and measurement of environmental parameters were done for a period of eighteen months to cover seasonal variation in epizootic occurrence. Conventional and molecular techniques were employed in the confirmation of the causative agents. Furthermore, virulence of the recovered bacteria was studied in vitro using similar fish species to confirm the causative agent of ulcerative infections in Nile tilapia at the Mtera dam. 50 bacterial isolates belonging to 13 genera were obtained. Virulence experiment confirmed that the causative agents of ulcerative infections in the dam were Aeromonas, and Pseudomonas species. Temperature, DO, Turbidity, and conductivity showed significant effects on the observed infections pattern in the dam. Occurrence of fish mortality and clinical symptoms were profound during the dry period. The presence of infectious bacteria in the fish samples indicate a potential health risks for consumers as bacteria such as Aeromonas hydrophila are associated with human infections. Fishers/consumers are advised to avoid ulcerative fish from the dam particularly during the dry season. The high number of the isolated opportunistic bacteria from the dam is an alert for proper fish health management to evade great losses in case of stress oriented disease outbreaks.