M.Sc. Dissertation
Fishing is one of the main economic activities in Zanzibar. A few fish dealers are transforming this sector into mariculture. Among farmed fish is milkfish. Diseases are among the most important limitations in development of mariculture. Among others, vibriosis, a zoonotic disease of fish caused by bacteria from the genus Vibrio, is reported to cause significant losses in the industry. This study aimed at establishing the occurrence of Vibrio cholerae and Vibrio parahaemolyticus in milkfish farms in Zanzibar, and the risk factors associated with their occurrence. A questionnaire was administered to collect information about pond management practices. Fish biodata and water quality parameters were measured from each pond involved. Three hundred and eighty (380) milkfish were obtained from 52 different ponds, 12 from Unguja and 40 from Pemba Islands. Swabs were collected from gills, intestine and kidney of sampled milkfish. Enrichment and biochemical tests were performed for preliminary identification of V. cholerae and V. parahaemolyticus. Genus specific PCR was used to confirm Vibrio species. Multiplex PCR was set to detect V. cholerae and V. parahaemolyticus. Almost one-third (32.1%) of all milkfish were found to be infected. Eighteen percent and 29.5% of sampled milkfish were positive for V. cholerae and V. parahaemolyticus, respectively. Some of the sampled fish (12.5%) were infected with both V. cholerae and V. parahaemolyticus. All preliminarily identified isolates were confirmed to be Vibrio species on multiplex PCR. Milkfish farming in Zanzibar adopts recommended pond management practices except few like pond liming. There is a good number of Vibrio species isolated from milkfish. Some pond management practices have shown a significant association with occurrence of Vibrio species. Improving managerial practices and careful handling of fish are some of the means to prevent an outbreak. A further study on detailed characterization of isolated bacteria and determination of their antimicrobial resistance is recommended.
MJNUAT and TRAHESA