Microbial quality of fresh fish in open-air urban markets : a case study of fresh Nile Tilapia (Oreochromis Niloticus) in Kaleerwe Market, Kampala - Uganda

Abstract

Fresh fish, particularly Nile tilapia (Oreochromis niloticus), serves as a critical protein source for Uganda's population, with per-capita consumption of 12.5 kg annually exceeding continental averages. However, inadequate cold-chain infrastructure and poor handling practices in informal urban markets pose significant food safety risks. This study evaluated the microbial quality of fresh Nile tilapia at Kaleerwe Market, Kampala, focusing on total viable counts, temporal contamination patterns, and prevalence of key foodborne pathogens. Thirty-two fresh tilapia samples were collected using randomized sampling during morning and evening sessions. Microbial analysis employed standard culture-based methods following ISO 4833 protocols, with swabs collected from skin, gills, and mouth for total viable count enumeration and pathogen identification using selective media. Statistical analysis utilized paired sample t-tests and one-way ANOVA with effect size calculations. Results revealed critical food safety violations across all tested parameters. Staphylococcus aureus contamination (1,427-2,400 CFU/g) exceeded EU safety limits by 14.3-24.0 fold, while Escherichia coli levels surpassed standards by 2.6-4.4 fold, indicating significant fecal contamination. Paired sample t-tests demonstrated highly significant temporal increases in bacterial loads (p < 0.001), with contamination rising 35.1-76.6% between morning and evening samples. Effect sizes were large to very large (Cohen's d = 0.8-1.8), demonstrating practical significance. Total viable counts for skin samples exceeded safety thresholds throughout both sampling periods. One-way ANOVA revealed no significant spatial differences between anatomical sites (p > 0.05), indicating systemic contamination. The study documents pathogen levels ranking in the 95th percentile globally for informal markets, representing the highest contamination documented in East African literature. Temporal contamination increases of 68-76% demonstrate rapid bacterial proliferation under ambient tropical conditions, highlighting fundamental failures in cold-chain management and hygiene practices. The systemic contamination pattern indicates that post-harvest handling represents the primary control point requiring comprehensive intervention. These findings provide essential baseline data for evidence-based policy development and underscore urgent needs for regulatory enforcement, vendor training, and infrastructure improvements in Uganda's informal fish markets to protect public health.