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Mosquitofish: A Natural Way of Reducing Mosquitoes in your Backyard

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Do you ever wonder how you can enjoy a backyard fish pond with the aesthetics of a few water lilies and ornamental aquatic plants without contributing to mosquito development? So often water features, including waterfalls, half barrels and fish ponds, create that peaceful oasis that we need to relax and just let the day’s difficulties drift away. However, all sense of peace can suddenly disappear as hundreds of mosquitoes begin to make you their dinner. Why? Hordes of mosquitoes are developing from the area you had taken so much time and money to create.

Often, well-intentioned backyard features contribute to mosquito development. Worst of all, the mosquitoes hatching from backyard sources are usually the type of mosquito that can carry mosquito-borne disease. In San Joaquin County, the disease of concern is West Nile virus, which can make some people very ill and can cause permanent paralysis and even death. How do you enjoy your backyard without producing mosquitoes? Obviously, dumping out any standing water is a given. It only takes a few teaspoons of water for mosquito development. San Joaquin County Mosquito and Vector Control District encourages the use of mosquitofish, Gambusia affinis.

Mosquitofish were first introduced in California in 1922 and have since spread throughout the state. They are a live-bearing minnow closely related to the common guppy. Mosquitofish are temperature dependent for reproduction, breeding from mid-spring to fall in the San Joaquin Valley. They reproduce at intervals of about six weeks, with an average of 50 young in a single brood. Mosquitofish are the primary biological control agent for the District.

Best of all, mosquitofish are available free to residents of San Joaquin County including all cities. Once mosquitofish become acclimated to the water, they consume about 100 mosquito larvae and pupae per fish per day.

Mosquitofish can be picked up at our office at 7759 S. Airport Way, Stockton, or call (209) 982-4675 for delivery to your property. The fish will also be available during the District’s mosquitofish giveaway from June 25 through June 29, 2018. See the District’s website,, in mid-June for giveaway location schedules. 

For more information on San Joaquin County Mosquito and Vector Control District, mosquitofish or mosquito control in general, please visit or call (209) 982-4675.

The Facts on Mosquitofish
• Common name: Mosquitofish
• Scientific/Latin name: Gambusia affinis
• Maximum length: Males .5 to 2 inches, Females 1 to 3 inches
• Color: Natural brownish gray
• Use: Control of mosquito larvae and pupae as they develop in water
• Water temperature preference: 77° to 86° degrees F; can survive 50° to 95° degrees F
• Compatibility: Not recommended for community tanks or ponds with other fish present. They are not recommended to mix with koi. Call the District for questions regarding koi and mosquitofish.
• Life span: 1 to 3 years
• Ease of keeping and breeding: Easy
• Feeding: Periodically feed fish with commercial floating goldfish flake food

Consider the following when using mosquitofish: Use mosquitofish for stocking in ornamental ponds, neglected or green swimming pools, animal water troughs, aquatic garden and landscape features. Protect fish from garden sprays, chlorine or other chemicals used to clean artificial ponds. New concrete ponds leach lime so they should be properly seasoned (filled, allowed to stand several days, drained and refilled) before introducing mosquitofish. If possible, provide large rocks in the deepest parts of the pond and vegetation for shelter from predators.

Written by: Aaron P. Devencenzi, Public Information Officer, San Joaquin County Mosquito and Vector Control District