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Scientists are developing a biological control method for malaria that uses larvae-eating fish to control mosquito populations in rain-fed pools.

Tanzania's Tropical Pesticide Research Institute (TPRI) is collaborating with the US-based Poseidon Science Foundation to investigate the best way to mass-produce and disseminate the fish embryos for eventual use in areas where malaria is endemic.

If successful the initiative will be used alongside insecticide-treated mosquito nets, pesticides and artemisinin drugs.

Using fish to control malaria is not a new idea, but the method has previously been restricted to permanent bodies of water. But in many high-risk areas malaria is seasonal, coming with the rains that create pools in which the larvae of malaria-carrying mosquitoes grow.

The Tanzanian fish species Nothobranchius guentheri is an annual species; the adults die off yearly, leaving their embryos in a state of suspended animation when the water recedes. The embryos hatch when the rainy season begins and feed on the mosquito larvae, which hatch around the same time.

The fish embryos can survive in pools as small as depressions made by elephants' feet.

"Once established in a particular depression, the fish will continue to come back year after year to feed on the mosquito larvae," says Shandala Msangi, the lead investigator of the programme at TPRI.

"This initiative to explore native annual fish populations as natural predators is part of [a] trend to explore indigenous technologies and resources," he adds.

Eliningaya John Kweka, senior scientific officer in medical entomology in TPRI's mosquito section says Tanzanian communities have a good understanding of the benefits of participating in mosquito control. "Therefore, we expect to have very good exciting results in this study in reducing malaria spread in Tanzania."

Storn Kabuluzi, controller of preventative health services and the former manager of malaria control in Malawi, says the method would be difficult and expensive to implement as cases of malaria are widespread.

According to Kweka, the major challenge is gaining significant, long-term support to carry out systematic studies and sustain a long-term programme. The Poseidon Science Foundation is supporting this initial programme and will need a consortium of participating organisations and countries to make this concept a reality, he says.

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