Pathology of Oreochromis Niloticus Due to Infections and Water Pollution in Kisumu and Homa Bay, Lake Victoria, Kenya

Abstract

The study assessed the health of Nile tilapia (Oreochromis niloticus) in the Winam Gulf in Kisumu and Homa Bay, Kenya, using descriptive lesions and histopathological semi-quantitative tools. The condition factor and hepatosomatic index were calculated based on the total fish weight, standard length, and liver weight. The liver, gills, and kidneys were collected from freshly killed fish, fixed in 10% buffered formalin, and processed using standard histopathological techniques. The overall condition factor of fish was 1.12 in Kisumu while those in Homa Bay ranged between 1.23 to 1.32 and the differences was statistically significant (p<0.05). The mean organ indices were higher in Kisumu (liver: 4.27, gill: 3.64 and kidney: 4.47) compared to Homa Bay’s (liver: 2.26, gill: 3.21 and kidney: 1.98). The most prevalent histopathological lesions in the liver were increased melanomacrophages centres aggregation (12.5%), hepatocellular fibrosis (9.7%), fatty liver degeneration (10.4%) and hepatocytic necrosis (9%). Those in gills, were leucocytic infiltration (12.5%), gill epithelial necrosis (11.8%), telangiectasia (11.1%), and gill lamellar fusion (11.1%). In the kidney the lesions were glomerular vacuolation and dilatation of the Bowman’s capsule (12.5%), and vacuolation and hydropic degeneration of renal tubular epithelium (11.8%). The study provides insight into the health status of fish in Kisumu and Homa Bay and demonstrates the histopathological changes and semi-quantitative scores of lesions in tissues caused by exposure to pollutants, infections by pathogenic microorganisms, and other factors that compromise the health of the fish. The findings indicate a need for monitoring the wild fish health and water pollution levels for socio-economic development and overall ecosystem protection in the region.