Why is very little research being done on the possibility of mosquito fish being used as a means of controlling the hatching of new eggs?
Actually there is a lot of scientific literature on the use of fish as a biological control of mosquitoes, usually through consumption of the mosquito larvae or pupae while they are in freshwater. The most common species used for this purpose are the guppy (Poecilia reticulata) and the appropriately named mosquito fish (Gambusia affinis). Other fish groups, like cyprinodontids (i.e. Aphanius species), tilapia and minnows will also eat mosquito larvae.
In addition, other freshwater predators, such as copepods, have been shown to be highly effective in killing mosquito in laboratory and field experiments, though results are sometimes inconsistent (see Lardeaux, 2008 “Biological control of Culicidae with the copepod Mesocyclops aspericornis and larvivorous fish (Poeciliidae) in a village of French Polynesia,” in Medical and Veterinary Entomology, vol 6, issue 1, pages 9-15, for a comparison of the anti-mosquito effect of these different groups).
The Lardeaux paper also describes the failure of the program: despite introduction of larvivorous animals, biting rates of mosquitoes did not significantly reduce, indicating some of the complications that can be associated with biological control programs.
However, in Vietnam, field studies have shown significant reductions of local Aedes mosquitoes associated with the presence of copepods in standing water sources, which shows the potential positive effects of incorporating natural biological control agents within part of an integrated vector control strategy (Nam et al., 2000 “National progress in dengue vector control in Vietnam: Survey for Mesocyclops (Copepoda), Micronexa (Corixidae) and fish as biological control agents,” in the American Journal of Tropical Medicine and Hygiene, vol 62, issue 1, pages 5-10).
Another example of successful introduction of fish as biological control agent comes from Ethiopia (Fletcher et al., 1992 “Control of mosquito larvae in the port city of Assab by an indigenous larvivorous fish, Aphanius dispar,” in Acta Tropica, vol 52, issue 2-3, pages 155-166).