Identification and antibiogram profiles of bacteria associated with diseased oreochromis niloticus in Lake Kariba, Zambia

Masters ThesisThe recent intensified aquaculture projects in Lake Kariba have brought about disease outbreaks in cultured Oreochromis niloticus. This has brought on an awakening to the scientific knowledge gap surrounding these events. This study aimed at identifying bacteria associated with diseased O.niloticus and establishes theirantibacterial resistance patterns. The diseased fish in cages were identified based on behavioural and physical abnormalities including swimming in circles, swimming in lateral or dorsal recumbency, ocular opacity, hyperpigmentation, fin erosions and ulcerations. A total of 25 sick and 4 apparently healthy fish were sampled. Samples from the liver, kidney, spleen, brain, abdomen, blood and ulcers were inoculated on 10% sheep blood agar and nutrient agar. Isolates were then classified by genera using standard culture and biochemical tests. The bacterial isolates were also tested for resistance to commonly used antibacterial compounds in aquaculture using the disc diffusion technique. The eyes, spleen and liver were found to have the highest number of pathologies, in descending order. A total of 15 bacteria genera were identified. Lactococcus/Streptococcus genera had the highest prevalence with 46.2% followed by Aeromonas at 11.5%. Multiple drug resistance was observed in all isolates, with two isolates each of Aeromonas and Lactococcus/Streptococcus exhibiting complete resistance to majority antibiotics tested. The results suggest that an increased biomass in diseased cages may be the main risk factor for the disease, with the immune and regulatory organs being first to succumb. The lake environment has been shown to be a mixing vessel of various microorganisms that are already showing multiple antibacterial resistance. Risk factors surrounding the presence of these bacteria genera must be accessedand a more comprehensive,comparative study in antibiotic resistanceon farmed,in contrast to wild species in the Lake Kariba.NORAD-NORHED-TRAHES