About Mosquitofish

Mosquitofish, Gambusia affinis, are an important part of our mosquito control program. They are a preventative biological control agent against mosquitoes that can reduce, but generally do not eliminate mosquito larvae from a water source like ornamental ponds, unmaintained swimming pools and animal water troughs. Many factors affect how well mosquitofish will work to minimize mosquitoes including the water’s condition, time of year and species of mosquito present.

Mosquitofish eat mosquito larvae as fast as they hatch from the eggs. They generally require no feeding and very little care. Mosquitofish do not lay eggs but give birth to live young. They breed throughout the summer and new broods are produced at about six week intervals. The young are about 1/4 inch in length when born and are ready to begin feeding immediately on mosquito larvae. Mosquitofish grow rapidly and reach a maximum length of about three inches.

During winter, water temperatures are too cold to release mosquitofish successfully. During March and April, outside temperatures start becoming warm enough for mosquitofish to survive, but mosquitoes that carry West Nile virus are not generally active yet. The District keeps a summer stock of mosquitofish and conducts property inspections of standing water sources from May to October to see if mosquitofish are the right treatment option for residents.

To learn more about mosquitofish you may read our brochure here.