General Contact Number: (530) 621-5567

Environmental Health

Image of Mosquito FishMosquito Fish (Gambusia affinis) - Defense from Mosquitoes
Mosquito fish (Gambusia affinis) are widely used to help reduce mosquito breeding. Their adaptability, hardiness, and ability to produce large numbers of young in a short time, has made them valuable biological control agents for mosquitoes.

Mature females measure two to two and a half inches long, and males from one to one and a half inches. Females can reach maturity in six to eight weeks. They bear three to four broods of young in a season; the first may number only a dozen, but later broods include 60 to 100 young. Under favorable conditions, mosquito fish live two to three years.

FEEDING:Image of Mosquito fish eating larva

Mosquito fish seldom need supplementary food. During the summer there is usually enough food in the pond, and in the winter their bodies slow down so much that very little food is needed. If they are given supplementary food, caution must be exercised. Overfed fish may not eat mosquito larvae, and any excess food that the fish do not eat can cause a bacterial bloom toxic to the fish.


Mosquito fish like the shelter of rocks and plants, but they do not thrive in heavily shaded ponds, and they tend to dwell in the sunny areas. In large ponds, the fish may even avoid mosquito infested shaded areas if they find or are provided other food. Mosquito fish are cannibalistic, so plants are necessary to help shelter the very young.

Normally six to ten fish are stocked in an average home pond, more if a large number of mosquito larvae are present. In some cases, the pond may need to be drained and cleaned, or treated with safe, state approved chemicals prior to introduction of the fish.

For information concerning mosquito fish availability, please call Environmental Management Dept. at (530) 621-5300 

Marin / Sonoma Mosquito & Vector Control District 

Links to Other Information

West Nile Virus Web Page 

WNV : El Dorado County Activity

How to Avoid Mosquito Bites

Symptoms of West Nile Virus