At the Marin/Sonoma Mosquito and Vector Control District, we offer residents an effective, natural and sustainable way to reduce mosquito production in certain water features by providing mosquitofish (Gambusia affinis) free of charge. These hardy little fish help stop mosquitoes before they ever become biting adults and are one of the best biological control tools available for mosquito management.

What Are Mosquitofish and How Do They Work?

Mosquitofish are small freshwater fish native to the southern and eastern United States that were introduced to California in the early 1920s specifically for mosquito control. They have since become an important part of mosquito management programs because of their ability to eat mosquito larvae in standing water.

Mosquitofish give birth to live young, and a single female can produce up to 100 young at regular intervals throughout the warmer months of the year. In ideal conditions adult mosquitofish can consume hundreds of mosquito larvae each day, significantly reducing mosquito populations in the water where they live.

These fish are surface feeders that are especially effective in shallow water and among dense vegetation where mosquito larvae thrive.

Where Mosquitofish Can Be Used

Mosquitofish work best in contained, artificial water sources that do not connect to natural waterways. These include:

• Ornamental ponds and backyard water features
• Unused or neglected swimming pools and spas
• Water troughs or barrels

 By placing mosquitofish in these types of water sources, mosquito larvae are eaten before they can develop into adult mosquitoes that bite people and animals.

Because mosquitofish are not native to California and can harm local ecosystems if released into natural waterways, it is important that they never be placed in creeks, rivers, lakes, or any water body that connects to those habitats. State regulations from the California Department of Fish and Wildlife prohibit private citizens from releasing mosquitofish into waters of the state without a permit.  

Not sure if your pond or water feature is a good fit for mosquitofish? Give us a call! We'll help determine if the habitat is appropriate, and if it is, we'll provide and stock the fish for you.

Care and Maintenance of Mosquitofish

Mosquitofish generally require minimal care. In established ponds they typically find enough food naturally and do not need supplemental feeding.

Mosquitofish can tolerate a wide range of water conditions, but they prefer areas that are not heavily shaded. Excessive leaf litter and very poor water quality can be harmful. Proper placement and basic maintenance of the water feature will help your mosquitofish thrive and continue to control mosquito populations.

How to Obtain Mosquitofish

Residents can request mosquitofish through our website at www.msmosquito.org or by calling our office (707) 285-2200. A District technician will stock your pond or other suitable water feature and leave a note on your door letting you know the fish have been delivered. Mosquitofish may also be picked up at our office during business hours (Monday through Friday, 7:00 AM to 3:30 PM).

Typical stocking rates vary by water feature size. For example, a small backyard ornamental pond may need just a few fish, while a larger neglected swimming pool may require more. Our staff can advise you on the correct number of fish to use based on your situation.

Mosquitofish are a powerful and natural tool in the fight against mosquitoes. By placing these fish in appropriate water features, you can reduce mosquito populations using biological means that are safe, cost-effective, and part of an integrated approach to mosquito management. If you have questions about mosquitofish or would like to request them for your property, visit our website at www.msmosquito.org or call our office 707-285-2200.