Mosquitofish (Gambusia affinis) are an environmentally friendly and extremely effective way of controlling mosquitoes. They are native to the backwaters and freshwater ponds of North and Central America and can live 2-3 years. Mature female mosquitofish can reach 7 centimeters (2.8 in) long, while males are usually smaller (about 4 centimeters or 1.6 in).
With a great appetite for mosquito larvae, mosquitofish also have special advantages. They usually stay close to the water surface where mosquito larvae are present. They multiply very fast and can tolerate tough conditions, including low oxygen content and elevated salinity. They can also tolerate a wide range of temperatures. For these reasons, they have been widely used to control mosquitoes to reduce the need for multiple pesticide applications.
Because mosquitofish are very prolific, they may compete with native fish species or prey upon other sensitive aquatic species in natural habitats. Therefore the District does not plant mosquitofish in these areas. It is against California Department of Fish and Game regulations for private citizens to plant mosquitofish in waters of the State without a permit. (Title 14 CCR, Fish and Game Code, Section 1.63, Section 6400, and Section 238.5).
To obtain mosquitofish and assistance, residents can call the District at (408) 918-4770 / (800) 675-1155 or enter a request for services on our website. Mosquitofish are delivered to County residents free of charge.
Residents who have an abundance of mosquitofish may call the District for arrangement to return them. Do not release mosquitofish into lakes, streams, rivers, or other natural habitats.
Residents who have water gardens or ornamental ponds can find helpful information from the following sources:
Helpful guides on maintenance of backyard water garden and ponds / Alameda County Mosquito Abatement.
Additional information on mosquitofish and possible mosquito sources / Los Angeles County West Vector & Vector-Borne Disease Control District.
Mosquitofish farming - Fish biologist Chris Miller / Contra Costa Mosquito & Vector Control District.