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, Santa Clara County
residents can call the District at (408) 918-4770 or enter a request for services
on our website. Mosquitofish are delivered to 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.