The effect of fish farming on the distribution and abundance of malaria vectors in Yala Swamp, Western Kenya
In this study the link between fish (Nile tilapia: Oreochromis niloticus) and the distribution and abundance of malaria mosquito larvae in five ecological sites of Yala swamp, western Kenya, was investigated. This was done in order to determine the prevalence and seasonality in the proliferation of malaria vectors and the relative importance of water quality parameters such as temperature, pH, dissolved oxygen, conductivity and turbidity on mosquito larval distribution. Two sites were identified namely area of high agricultural activities (AHAA) and area of intact primary vegetation (AIPV). The breeding habitants inspected for the presence of malaria vectors in the AHAA included a control pond, a treated pond, a fish pond and standing water pools. Swamp ground was inspected in the AIPV. The species of mosquitoes identified were Anpheles gambiae. Anopheles funestus and Cuulicines. An. gambiae accounted for 57.4% of the total mosquitoes identified in both field and semi-field experiments, with no significant difference in density between seasons. An. funestus was second in abundance at 25.8% followed by Culicines which only accounted for 16.8% of mosquito species in Yala swamp during the study. Apart form temperature, the distribution and abundance of mosquito larvae was significantly associated with water quality parameters such as pH (r= -0.48; P<0.01), Do (P<0.01), Conductivity (r = -0.11; P<0.01) and Turbidity (r = -0.57; P<0.01). Although fish was observed pursuing and feeding on mosquito larvae, mosquito population reduction in fish-seeded pond was not statistically significant (P>0.01). The occurrence of the most efficient primary vectors of malaria in Yala swamp could accelerate the burden of malaria in the region if appropriate action is not taken.