Prevention of disease transmission by malarial mosquitoes and other insects requires a multifaceted approach, which includes killing mosquitoes with pesticides and larvicides. Biological control has now regained interest because of the resistance of mosquitoes to pesticides and to anti-malarial drugs, including artemisinin. The concept of using larvivorous fishes as an inexpensive biological control is an old concept, with some past successes. However, the introduction of the mosquitofish, Gambusia affinis, in new habitats has devastated indigenous freshwater organisms. Although local species of fish have been studied extensively as a means of larval control, their effectiveness is limited only in permanent bodies of freshwater. Malarial mosquitoes are generally found in higher elevations in temporary pools that dry up seasonally, thus negating any initial control provided by larvivorous fishes or even chemical control agents. When the water dries up, the conventional fishes are decimated while the mosquitoes enter a dormant state until the next rains. Moreover, these malarial areas are generally inaccessible making vector control expensive and sporadic at best. The ideal control method in such habitats should be organisms that prey on mosquito larvae and can maintain permanent fish populations in temporary habitats so as to be present when the rains come and as the hibernating eggs of mosquitoes begin to hatch.

Annual fish represents a unique class of fishes that survive in alternating dry and wet seasons by entering a state of dormancy or diapause, just like in mosquitoes. The adults are decimated when the water dries up. The embryos, buried in the substrate during the previous breeding season, go through various phases of suspended animation or diapause to survive drought. When the rainy season arrives, these embryos hatch to feed on mosquito larvae that also hatch at about the same time period. These fish are known to survive even in small depressions, such as water-filled elephant hoof prints. Annual fish are endemic to Africa and South America. The most extensively studied are those that belong to the genera Nothobranchius that occupy a wide range of habitats in Africa. N. guentheri is an ideal fish for a malaria vector control program because: (1) it can survive in temporary pools of freshwater; (2) its small size allows it to seek prey in between leaves and grass in shallow areas; (3) small size also makes them less suitable to be used as food source by local human population; and (4) the species does not survive in permanent bodies of freshwater and thus pose no threat to other indigenous fishes.

Scientists from Poseidon Science Foundation have been working on developing convenient methods of mass producing the eggs and new methods of disseminating the embryos for eventual use in vector control. Moreover, the last three decades of research has enabled a better understanding of the life cycle of annual fish. Poseidon's collaboration with Tanzania's Tropical Pesticide Research Institute (TPRI) presents a unique opportunity to make the first formal attempt to use these fishes for biological control. Since N. guentheri is native to Tanzania, the regulatory problem of new species introduction is not an issue. "This undertaking is pivotal. Once we are able to demonstrate the usefulness of annual fish for vector control in Tanzania, we can then expand the same concept to other African countries where other native populations of annual fish exists," says Jonathan R. Matias, executive director of Poseidon. The project involves studies on methods of field introduction and monitoring of larvivorous activity in controlled test ponds. Eventually, this effort will expand into mass production of the fishes locally and dissemination to malarial areas of Tanzania. "The collaboration with Poseidon Sciences Foundation on vector control research offers an opportunity to test novel, non-chemical, renewable and sustainable concepts that can help in vector control in Africa. We, at TPRI, are looking forward to working with Poseidon into this scientific endeavor," says Shandalam Msangi, the lead investigator at TPRI on this programme.

POSEIDON SCIENCE FOUNDATION (Poseidon) is the non-profit organization of the Poseidon Sciences Group. Among PSF's primary missions are: (1) protect and preserve our aquatic environment; (2) develop livelihood technologies for coastal communities; and (3) develop biomedical and bio-industrial innovations derived from our aquatic resources.

Tropical Pesticide Research Institute (TPRI) is a multidisciplinary institute operating under the Ministry of Agriculture and Food Security of Tanzania and is responsible for pesticide regulation, health and safety, pest management and scientific research. TPRI started research work on Integrated Vector Management of mosquitoes and tsetse flies since 1946. TPRI collaborates with Government at all levels and across sectors, academic and service institutions, and NGO's to promote sustainable rural development through intervention in the different areas.

Source

Jonathan R. Matias, Executive Director
Poseidon Science Foundation
122 East 42nd Street, Suite 1700, New York, NY 10168

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