Pathological changes associated with pollution and endoparasites in Nile perch and Tilapia in Lake Victoria, Kenya
Kamundia, Patrick W
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Fish are important source of food for humans and animals in Kenya. The Lake Victoria is a major source of fish where decline in fish catches has been reported leading to concerns by the stakeholders over the future availability and quality of the fishing the lake. Among the factors thought to may have played a role in this decline are various types of pollutants going into the lake. However, this role and any associated fish lesions have not been investigated and were the main objectives of this study. The study assessed the community's knowledge on pollution and the gross and histopathological lesions in Oreochromis niloticus and Lates niloticus landed fish. The prevalence of endoparasites in fish and their pathological effects were also investigated in Dunga in Kisumu, Homa Bay and Sindo. Questionnaires and focus group discussions (FGD) were used to assess the lake pollution and fish production at Homa Bay and Sindo site while live fish samples were also taken from the two sites. Standard necropsy procedures were carried out on the fish and gross lesion recorded. Tissue samples taken were preserved in 10% formalin for histopathological processing and the fish were examined for endoparasites that were preserved in 70% alcohol and identified. Blood smears were taken from fish, fixed in methanol, stained in Giemsa and examined for haemoparasites . The questionnaire and the FGD reveal that Oreochromis niloticus, Lates niloticus and Rastrineobola argentea were the most important fish in the lake. The results also showed that fish production had declined due to overfishing, pollution, increased human population pressure, use of illegal fishing methods and climate change. Major sources of lake pollutants reported were raw sewage, industrial effluents, oil spills, and soil erosion and application of fertilizers, More pollutants were reported in Homa Bay than Sindo. Necropsy and histopathology studies revealed deformities of the dorsal fin, head and heart; fibrosis, hemorrhages, bile imbibition, gray foci and fatty liver in the liver; testicular hemorrhages and cysts and malformed hearts were observed in Homa Bay and Sindo. Gross lesions between 0. niloticus and L. niloticus had an association (p<0.018). Hepatic fibrosis, fatty degeneration and hemorrhages in the liver; clubbed secondary lamellae and aneurysm in the gills; increased melanomacrophage aggregations, hydrophic degeneration and vacuolation of the renal tubules in the renal system; and disorganization of testicular lobules and testicular hemorrhages in the testis were the major histological lesions. Previous studies have shown that pollutants in water are associated with some of these lesions. Kidney, liver, spleen and stomach granulomas, myocarditis, and epicarditis were also observed. Histological lesions in the two fish species indicated no association (p>0.05). Lates niloticus were 1.75 and 1.38 times at risk of having overall gross and histological lesions in Homa Bay than in Sindo and 2.6 and 2.1 times at risk of having renal and testicular tissue lesions in Homa Bay than in Sindo (p<0.05). The 0. niloticus were 1.2 times at risk of having gastrointestinal tract lesions in Homa Bay than in Sindo (p<0.05). The condition factor indices indicated healthy 0. niloticus at 1.43 and 1.1; and L. niloticus at 1.57 and 1.25 in Homa Bay and Sindo, respectively. Pathological lesions observed in Oreochrornis niloticus and Lates niloticus could affect their health, welfare being, reproduction and lake fish production. Prevalence of endoparasites in 0. niloticus in Dunga were 41.4%, Homa Bay 12.5% and Sindo (4.5%). In L. niloticus the prevalence were 36.0% in Dunga, 13.3% in Homa Bay and 13.3% in Sindo, respectively. Three nematode genera Procamallanus, Carnallanus and Contracaecum) and one Acanthocephalan (Acanthocephala spp.) were recovered from the lumen of the gastrointestinal tract of the study fish, Contracaecum being the most prevalent. Histological sections of the liver, spleen and stomach showed endoparasites lodged in tissues where they caused variable pathological lesions. Trypanosoma species were observed in the blood smears of a sample of 0. niloticus from Homa Bay. In conclusion, the some sources of pollutants that enter Lake Victoria were documented in this study. Some of the gross and histological lesions noted in the fish from the lake were attributable to pollutants and possibly endocrine disruptors. Parasite prevalence's were higher in sites presumed to be polluted. More research on specific types and levels of pollutants and effects on the fish are recommended.