PLEASE NOTE: The District remains closed to the public and in-person fish pick up remains unavailable. Contra Costa County residents may request mosquitofish from the District online or by calling 925-685-9301. Upon receiving your request for mosquitofish, a District employee will follow up with you and make an appointment for an inspection. During the inspection, the District employee will determine if the water feature is an appropriate location for the fish. If the location is appropriate for mosquitofish, the District employee will place fish in the water feature. If, for example, the water feature is found to be producing more mosquito larvae than the fish can initially handle, the District employee will provide assistance and advice on the appropriate action to mitigate the mosquito issue.
This hearty species of guppy can survive various water quality conditions and temperatures as well as reproduce often. Learn more about caring for mosquitofish by clicking here.
Mosquitofish may be used in ornamental ponds, horse troughs, stock ponds and other artificial water bodies and may not be placed by the public in creeks or natural water sources.
How Do Fish Control Mosquitoes?
As a natural predator of mosquito larvae, mosquitofish have been used for mosquito control purposes throughout the world for many years. They have a voracious appetite. Each fish can eat several hundred mosquito larvae per fish per day! More than 1 million of these fish are produced each year at the Contra Costa Mosquito Vector Control District's mosquitofish production facility, which requires specialized care in a specific, controlled environment. These fish are routinely stocked by technicians to control mosquito populations throughout the county. They are often placed in neglected swimming pools (pools that are not chlorinated or filtered). Pools in this condition can potentially produce up to 1 million mosquitoes per swimming pool, even partially filled pools. Residents can also place these fish in their own neglected swimming pools (ideally, the Contra Costa Mosquito & Vector Control District would appreciate residents properly maintaining their swimming pools by ensuring they are chlorinated and filtered).
By law, only vector control technicians can place fish in water sources other than those located on private property. Some common 'sources' or sites where these fish are stocked include; artificial lakes, irrigation ditches, storm channels, and natural industrial ponds. Of course, we encourage residents to get free fish from our District to take home and place in their own backyard pond, horse trough, or neglected swimming pool.
To avoid competition with sensitive native amphibian and fish species, we do not stock mosquitofish in habitats where such species are known to be present.