They eat mosquito larvae as fast as they hatch from the eggs laid by mosquitoes in rafts on the surface of the water. They require no feeding and care is limited to protecting them from garden sprays and from chlorine or other chemicals used to clean the pond. The district also stocks thousands of these fish each year in artificial lakes, reservoirs, waste water disposal lagoons, natural creeks and drainage channels to eliminate the need for frequent spraying with mosquito pesticides. The mosquito fish, Gambusia affinis , is a small guppy-like fish used to control mosquito larvae. Each female can produce three to four broods in her lifetime, and each brood can vary from 40 to 100 young.
Birth usually occurs during the warm spring and summer months.
Mosquito fish are hardy and can live in many types of water habitats for several years. The Shasta Mosquito and Vector Control District plants thousands of mosquito fish each year in ponds, swamps, unused swimming pools, canals, creeks, water troughs, etc. which help provide mosquito control. The fish inhabit the shallow edges of ponds and creeks because of the abundance of food and to escape predation by larger fish such as bass and perch.