Pathological Changes in Oreochromis Niloticus and Lates Niloticus in Kisumu and Homa Bay, Lake Victoria, Kenya

Abstract

Histopathology as a tool for assessing fish health in an aquatic system is an important, but has not been extensively used in East Africa. Due to scarcity of data on the histopathology of the Oreochromis niloticus and Lates niloticus species in the Lake Victoria, the present study was conducted to determine the prevalence of gross and microscopic lesions present in the live fish caught in Kisumu and Homa Bay, and identify those attributable to pollution. The study was carried out in 2008-2010, and a total of 123 fish; 72 Oreochromis niloticus and 56 Lates niloticus were sampled. The weight and length of each fish measured and biometric indices calculated. Gross lesions were identified and note at necropsy and histopathology samples collected from selected organs collected and preserved in formalin, processed into slides and examined for lesions. Forty nine O. niloticus were found to have gross lesions at necropsy (69%, 95% C.I. 57.5-78.5), while histopathological lesions were detected in 56/71 (78.9%, 95% C.I. 68.0-86.8). Twenty four L. niloticus were found to have gross lesions at necropsy (46.2%, 95% C.I. 33.3-59.5), while histopathological lesions were detected in 32/52(61.5%, 95% C.I. 47.9-73.5). The liver, gills and kidney had the highest prevalence of lesions. The condition factor and the hepatosomatic indexes in the Oreochromis niloticus were 1.43 and 2.02 respectively, while those of Lates niloticus were 1.2 and 1.6, respectively. The present findings indicate that the Oreochromis niloticus had more lesions than L. niloticus. The biometric indices of the two species show the fish are healthy, however the gross and histopathological lesions which are bio-indicators of the presence of stressors such as disease, trauma and pollution suggest the fish health is threatened. Further studies should be done to determine the extent to which the histopathological alterations affect the health of fish