Mosquitofish (Gambusia affinis) are indispensable to our mosquito control program in Lake County. The fish eat mosquito larvae. Mosquitofish are provided, without charge, to the public for ponds, unused swimming pools, animal watering troughs, and other water features. They require minimal feeding or care, other than to protect them from garden sprays, chlorine, chloramines, or other chemicals, and predators such as raccoons, cats, opossums, herons or egrets. Mosquitofish generally live peacefully with other pond fish.

Life Cycle

These fish do not lay eggs but give birth to well-developed and very active young. Therefore, they require no special environment for depositing and hatching eggs. Mosquitofish breed throughout the summer producing a new brood at monthly intervals. The newborn fish are approximately one-quarter inch in length and are immediately ready to begin the work of eating mosquito larvae. Gambusia grow rapidly, reaching a maximum size of about three inches. The fish become sexually mature when 4-5 months old; the earliest broods of the season are born in April to May. Mosquitofish can live 2-3 years.

Controlling mosquitoes with fish

Keeping a healthy population of fish in your pond or water feature is the first line of defense against mosquitoes. Goldfish and koi will feed on mosquito larvae but are not as effective as mosquitofish or other top-feeding minnows. Overfeeding your fish will also reduce their effectiveness for mosquito control.

How to obtain mosquitofish

To obtain free fish, call or visit the District office. Mosquitofish are normally available from May through October. The District is always glad to provide mosquitofish to County residents, even on repeat calls, to encourage the biological control of mosquitoes in ponds and other permanent water features.