Benton County Mosquito Control District

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Distribution
Life history
Impact of introduction
What to do if you want mosquitofish

Gambusia Affinis
Mosquitofish

Distribution
The natural range of the mosquitofish was New Jersey south to Florida and the Gulf of Mexico, and central US from southern Illinois to Alabama and Mexico. Gambusia affinis, the western mosquito fish is no longer considered the same species as the eastern mosquitofish, Gambusia holbrooki. G. affinis and G. Holbrooki have been introduced indiscriminately throughout the world in temperate and tropical climates for mosquito control wherever mosquito-born diseases pose a threat to human health. For example, mosquitofish have been introduced into southern European countries, Germany, Thailand, Africa, Russia and Argentina. Gambusia have been introduced or are native to at least 43 states in the US.

In Washington, Gambusia are not widely distributed. Gambusia are known to be present in Benton and Clark counties. Gambusia have been located in other areas as well, but as for all the sites of this fish, it is still unknown.

Life history
Gambusia belong to the Poeciliidae family (live bearers), such as guppies, topminnows and killfish. Mosquitofish prefer quiet, shallow ponds, lakes, ditches, drains, marshes and sluggish creeks with clear water and aquatic vegetation. They prefer warm water temperatures and can tolerate water temperatures between 40 and 100 degrees Fahrenheit. Their life span is short, probably less than 15 months. They are ovoviviparous (live bearers). Gambusia reach maturity in 4 to 10 weeks. Each female can produce three to four broods in her lifetime, and each brood can vary from 40 to 100 young. The young are born in spring and summer when they are about 0.4 inches long. Adult length ranges from 0.8 to 2.5 inches. Mosquitofish eat a variety of macro-invertebrates, including mosquito larvae, other small insect larvae, zooplankton and aquatic plants such as algae and diatoms. Gambusia are aggressive and may also feed on fish fry. Feeding is at the water’s surface.

Gambusia have been used for mosquito control in the US since the early 1900’s. Various agencies throughout the world have developed stocking guidelines for mosquito control in swimming pools (abandoned), ornamental pools, ditches, wetlands, mine pits, storm water and waste water disposal lagoons, natural creeks, animal watering troughs and small seasonal or permanent ponds. Recommended stocking rates in the US range from 15-100 fish for back yard ornamental ponds to 2,500 fish/acre for small ponds and ditches. Reports from mosquito control organizations indicate that the greatest problem associated with the inability of Gambusia to control mosquito larvae are aquatic vegetation, inadequate fish numbers or a lack of distribution by the fish in a water site.

Gambusia do not provide 100% control in all types of mosquito habitats, but in certain situations, it is believed that they can help reduce mosquito populations.

Impact of introduction
Mosquitofish can compete with other animals for available resources and Gambusia have been blamed for predation of the fry of other fish. Importation and transportation of Gambusia in Washington State requires approval and a permit by the Washington State Department of Fish and Wildlife (WDFW). Benton County Mosquito Control has a permit to transport Gambusia affinis. But only certain sites meet the requirements to have Gambusia introduced. Introduction is determined on a case by case basis to insure that the mosquito fish are introduced into an isolated site (no connection to lakes, rivers, streams or canals) where they may have a positive impact upon the existing or potential mosquito populations.

What to do if you want Mosquitofish
If you feel that you have a water site that may benefit from the addition of Gambusia you have some options available.

You can give us a call at (509) 967-2414 and make a request to receive Gambusia. There is a form that must be reviewed and signed before we can deliver the fish and we will have a few questions pertaining to the water site. We will mail, fax or email the necessary form and after we receive the completed form back, we will put you on a list for delivery.

Download Gambusia Acceptance Form

You can print out a copy of the Gambusia Acceptance Form by following the instructions below, and mail or fax us the completed form. Then you will be placed on the delivery list.

Download Gambusia Acceptance Form

1. Right click on the link above.
2. Select "Save Target As" from the menu.
3. When you are given the option to either save or open the file, select "Save" and select the folder you wish the file to be saved in.
4. Once the file is downloaded, open it, and print it out.
5. After filling out the form, either mail it to our mailing address listed below, or fax it to us with the fax number listed below.

Mailing Address:

Benton County Mosquito Control

4951 W. Van Giesen

West Richland, WA 99353

Fax: (509) 967-2490

Thanks to the Washington Department of Fish and Wildlife for information provided on Gambusia affinis.