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Dual tool: Tilapia offers food and disease control

KENYA - The Nile tilapia (Oreochromis niloticus ) is already a popular food fish in Kenya. But it may also be a great tool in mosquito control, which helps to reduce the spread of the infectious disease malaria.

A study, published in the BioMed Central Public Health Journal, has found that O. niloticus can have a significant impact on reducing mosquito densities.

The fish was introduced into abandoned fishponds at an altitude of 1,880m and the effect on the numbers of mosquito immatures were measured over a six month period. An untreated control pond was also used for comparison.

The numbers of mosquito larvae immediately dropped in the treated ponds, but they increased in the other control ponds where no fish were present. This increase was apparently due to climatic factors. Mulla’s formula was applied which corrects for that natural tendency to increase.

However, after 15 weeks the fish's existence in the treated ponds had caused a 94 percent reduction in two types of mosquitoes. There was also more than a 75 percent reduction in another type of mosquito. Overall the tilapia dramatically reduced mosquito larval densities in the fishponds for at least six months - the reduction was directly linked to their predation.

During the investigation, all ponds were regularly cleared of emergent vegetation and fish re-stocking was not needed. Significant auto correlation was removed from the time series data, and t-tests were used to investigate within a pond and within a mosquito type any differences before and after the introduction of O. niloticus.

This study is the first field trial data on O. niloticus for malaria mosquito control and shows that this species, is an apparently sustainable control tool.
It offers dual benefits to rural communities in Kenya - as a source of protein and income and as a malaria control method.

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