Mosquitofish provided by the County of Santa Clara Vector Control District are intended for mosquito control only and should not be introduced into potential mosquito breeding sources by anyone other than the certified mosquito control technicians.


The District provides FREE mosquitofish to all of Santa Clara County residents for placement in manmade locations such as:​

  • ​Ornamental ponds
  • Unmaintained swimming pools/ jacuzzi
  • Watering trough
  • Fountains
  • Rain barrels​​

About Mosquitofish

Mosquitofish (Gambusia affinis) are small fish in the guppy family that are natural predators of mosquito larvae and pupae, making them an environmentally friendly alternative to mosquito control without the use of chemical insecticides. This method is referred to as biological control and is part of our integrated pest management program (IPM).

Gambusia are easily maintained and have a broad tolerance to a wide range of environmental conditions such as poor food supply and temperature changes. Mosquitofish are compatible with most ornamental pond fish such as goldfish, koi, and carp but live best with fish their own size, as larger fish might eat them.

Males are slimmer than females and grow to a maximum length of 1.5 inches. Females have a larger body than males, give birth to live young, and grow to a maximum length of 2.5 inches. Fry are only ¼ inch in size and reach sexual maturity in six to eight weeks. The small size of mosquitofish allows them to inhabit shallow waters and penetrate dense vegetation where mosquito larvae and pupae tend to hide. 

Mosquitofish sizes: female : 2.5 inches, male: 1.5 inches, Fry: 1/4 inch.

Mosquitofish live between two to three years and maintain population levels that fit their environment. Overbreeding is of no concern with mosquitofish.

Mosquitofish Care

While mosquitofish are a hardy species, water temperature and water quality must be considered before adding them to a new environment. Take the following steps to help ensure your mosquitofish survive in their new environment.


Treat Tap Water with A Water Conditioner

Mosquitofish cannot survive in water that is treated with chlorine or chloramine. Following the label, treat tap water with a water conditioner sold at your local pet store. Make sure the water conditioner treats chlorine, chloramines, and ammonia.

Help Them Acclimate to Their New Environment

Fish will be given to you in a plastic bag. When you get home, immediately float the bag in the pond, fountain, etc. Wait 20 minutes before releasing into the new environment.

Provide Protection

Fish prefer sunlit areas and do not thrive well in heavily shaded locations. Provide large rocks and vegetation for shelter and to help hide from predators such as raccoons​ and opossums.


Limited Feeding Required

Mosquitofish of all ages have strong appetites for mosquito larvae; they also eat small invertebrates and aquatic vegetation. Although mosquitofish may not need supplementary food throughout most of the year, mosquito larvae may be scarce during winter. In this case, fish flakes may be given in amounts specified by the label. Also consider feeding fish flakes if fish are placed in a newly constructed or recently cleaned water feature.

Provide a Healthy Habitat

Presence of algae can be a good habitat for fish if properly maintained, but if it gets too thick, mosquito breeding can still occur, and fish will be unable to reach mosquito larvae. If considering the use of herbicide, following the instructions on the label of materials used.

If using a wine or whiskey barrel for fish, ensure to soak and flush out barrel several times before adding fish or plants. They can leach harmful chemicals into the water if not flushed or lined.

How to Obtain Mosquitofish and Guidelines Info

Mosquitofish are in stock between February and October. Please call our office at (408) 918-4770 or submit a service request to check availability and request delivery.

Mosquitofish Stocking Guidelines


Number of Mosquitofish

Ornamental pond

4 – 6 fish

Swimming pool

10 – 15 fish

Wine barrel

3 – 4 fish

Water trough

4 – 6 fish

Additional Resources

Mosquitofish Maintenance Information

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