Using Fish to Control Mosquitoes
PHONE
800-231-3236 (toll free)
707-285-2200 (office)
707-285-2210 (fax)
ADDRESS
595 Helman Lane
Cotati, California
94931-9736
HOURS
Monday through Friday
7:00AM to 3:30PM
Marin / Somona Mosquito & Vector Control District personnel provide mosquito fish to the public to help control mosquito larvae in container and pond habitats. Proper pond design reduces mosquito breeding habitat and enhances mosquito fish production.
Mosquito fish (Gambusia affinis) are widely used by public health and mosquito control agencies throughout the world to help reduce mosquito breeding. Their adaptability and hardiness, and their ability to produce large numbers of young in a short time, has made them valuable biological control agents.
![[Mosquito fish]](images/mosqfish.gif)
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
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.
POND DESIGN AND MAINTENANCE
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.
Proper pond design helps reduce mosquito breeding habitat and enhances mosquito fish production. Manuals on pond design are available from the U.S. Department of Agriculture's Soil Conservation Service ("Agricultural Handbook No. 590"), and the California Department of Fish and Game as well as commercially. Run-off waters should not be allowed to enter the pond. This prevents contamination by silt, fertilizers and pesticides. The pond should be at least six inches deep and be cleaned periodically to remove leaves and debris. Plastic wading pools seldom make suitable fish ponds because they are shallow and allow the water get too warm. High temperatures deplete the oxygen supply, causing bacterial development and enhancing algal growth.
Agricultural Handbook No. 590
http://aqua.ucdavis.edu/Special_topics/Pond_construction.htm
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.
A limited amount of algae may benefit mosquito fish, but too often it indicates other problems. Correction of the conditions causing algal growth is not always simple, and may require repeated draining, cleaning and changing of the water. Some algicides are toxic to fish, so they should be used only on advice of a knowledgeable person. Materials and instructions may be obtained from local tropical fish shops or garden supply centers.
TRANSPORTATION
Transportation must be done correctly to avoid weakening or killing the fish. Metal containers are not recommended because they easily conduct heat and can warm the water excessively. Some materials are highly toxic to fish. Plastic buckets or plastic bags work well for transporting fish short distances. A large surface air supply is essential, so be careful not to fill containers too full of water. Do not use sealed containers without adequate air space. Keep plastic containers out of the sun during transportation, and introduce fish as soon as possible. When placing fish into the pond, you may add pond water to the container, or place the container in the pond to allow the water temperatures to equalize so as not to shock the fish.
ABOUT THE DISTRICT
Objective: To provide an abatement program directed primarily toward the prevention, elimination or control of aquatic sources leading to the production of mosquitoes capable of disease transmission, or serving as a public nuisance.
Approach: Under the California Health and Safety Code, mosquito abatement districts are empowered to take all necessary and proper steps for elimination and extermination of mosquitoes. District personnel make routine inspections of countless mosquito sources, such as ditches, channels, lagoons, drain lines, marsh areas, creeks, lakes, flood control basins, utility vaults, catch basins and fish ponds. If mosquito production is found, they take action to control or eliminate the problem. This activity often goes unnoticed by the general public, except for persons directly involved with specific problems.
Your Responsibility: Chapter five of the California Health and Safety Code requires that any mosquito production site declared to be a nuisance must be abated by the property owner.
If you have a pond and would like fish or an inspection, please call the District Office.