Identifying bacteria associated with diseased Oreochromis niloticus in Lake Kariba, Zambia
##plugins.themes.bootstrap3.article.main##
Abstract
Abstract. Sakala T, Mdegela RH, Hangombe BM. 2022. Identifying bacteria associated with diseased Oreochromis niloticus in Lake Kariba, Zambia. Bioteknologi 19: 62-70. The recent intensified aquaculture projects in Lake Kariba, Zambia, have brought about disease outbreaks in cultured Oreochromis niloticus (Linnaeus, 1758). This study aimed to identify bacteria associated with diseased O. niloticus and establish their antibacterial resistance patterns. Caged fish were identified as diseased based on behavioral 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 healthy fish were sampled. Samples from the liver, spleen, brain, abdomen, kidney, blood, and ulcers were inoculated on 10% sheep-blood agar and nutrient agar. Then the isolates were classified by genera using biochemical tests and standard culture. Furthermore, the bacterial isolates were tested for resistance to commonly used antibacterial compounds in aquaculture using the disc technique; the spleen, eyes, and liver had the highest number of pathologies in descending order. A total of 15 bacteria genera were identified, where Lactococcus/Streptococcus genera had the highest prevalence with 46.2%, then Aeromonas at 11.5%. All isolates have been observed to have multiple drug resistance, with two isolates, each of Lactococcus Streptococcus and Aeromonas exhibiting complete resistance to most antibiotics tested. The results suggest that 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 is a mixing vessel of various microorganisms that show multiple antibacterial resistance. Therefore, risk factors surrounding the existence of these bacteria genera must be accessed, and a more comprehensive, comparative study in antibiotic resistance on farmed, in contrast to wild species, in Lake Kariba, Zambia.