IMPACT OF WATER QUALITY AND ANTIMICROBIAL RESISTANCE ON THE PATHOGENS OF FARMED FISH (Oreochromis niloticus) IN UASIN GISHU COUNTY, KENYA

Abstract

Aquaculture is increasingly recognized as a sustainable strategy for meeting the rising global demand for protein, particularly in developing countries such as Kenya where capture fisheries are under pressure. Despite its potential, aquaculture growth is hindered

by poor water quality and the emergence of microbial and parasitic infections that com- promise fish health, productivity, and ultimately farmer livelihoods. This study evaluated

the impact of water quality on the diversity and prevalence of microbial and parasitic or- ganisms in cultured fish, and examined the antibiotic susceptibility of bacterial isolates

from aquaculture systems in Uasin Gishu County, Kenya. A longitudinal survey was conducted from May 2023 to April 2024 across five farms and thirteen ponds. Monthly assessments of water quality parameters (temperature, pH, dissolved oxygen, turbidity,

and nutrient concentrations) were performed following standard APHA protocols. Con- currently, fish samples were collected for microbial and parasitic screening. Bacteria

were isolated through culture-based methods and identified morphologically and bio- chemically in accordance with Bergey’s Manual, while parasites were identified micro- scopically. Antibiotic susceptibility testing employed the Kirby–Bauer disc diffusion

method using commonly applied antibiotics. Statistical analyses included chi-square tests for associations between infection prevalence and host/seasonal variables, one-way ANOVA to evaluate differences in water quality parameters, and logistic regression to

determine significant predictors of infection. A total of 154 bacterial isolates were recov- ered, with Escherichia coli (34.8%) and Pseudomonas aeruginosa (21.7%) being most

prevalent. Parasitic infestations, primarily protozoans and helminths, were concentrated in gills (p < 0.001) and showed significant seasonal variation, with peak prevalence during warmer months. Logistic regression revealed that organ type, bacterial species, and water quality parameters were significant predictors of infection (p < 0.05). Poor water quality, marked by low dissolved oxygen and elevated ammonia, was strongly

associated with increased pathogen load. Importantly, several bacterial isolates exhib- ited multi-drug resistance, raising concerns about environmental contamination and the

spread of antimicrobial resistance.This study provides critical insights into the complex interactions between water quality, pathogen diversity, and fish health in aquaculture

systems. It demonstrates that disease occurrence is not random but is strongly influ- enced by environmental conditions and farming practices. The findings highlight the

need for routine water quality monitoring, improved pond management, and the adop- tion of biosecurity measures to reduce infection risks. Furthermore, the detection of

resistant bacteria underscores the urgency of promoting responsible antibiotic use to

safeguard fish health and protect public health. Overall, the study emphasizes an inte- grated approach that combines environmental stewardship, sustainable husbandry prac- tices, and prudent health management to ensure the long-term viability of aquaculture

in Uasin Gishu County and similar settings.