, Gambusia holbrooki.
Tuesday, August 26, 2008
Introduction
In an effort to control mosquitoes with less reliance on the use of pesticides, the County of York, Mosquito Control Division utilizes several approaches. In an integrated approach to pest control, one aspect is the use of biological control agents. An example of a biological control agent for mosquito control is the mosquitofish, Gambusia holbrooki. When used correctly it is an efficient, cost-effective, and environmentally sound method for the control. The Mosquito Control Division has constructed two 30,000 gallon tanks shown here. Each holds several thousand mosquito fish. Our intention is to breed these fish and stock them into areas that breed mosquitoes. The species is Gambusia holbrooki. We are one of the nine government fisheries that produce fish for stocking in Virginia, and the only fishery in Virginia producing Mosquito Fish.
Mosquito Biology
There are nearly sixty different species of mosquitoes in York County, and they may be found in almost as many varieties of habitat. All have one point in common. They all require, as part of their life cycle, standing water in which to develop. It is in water where, as larvae and pupae, they spend a major part of their life cycle. During these aquatic stages of their development mosquitoes are most susceptible to control. It is at this point that mosquitofish, once introduced, will opportunistically consume mosquitoes.
Mosquitofish Biology
Gambusia holbrooki, a member of the live-bearer family Poecilliidae, is a species native to Virginia and widely distributed in the Chesapeake Bay system.
The mosquitofish thrives in a wide variety of water types, being very tolerant of high water temperatures as well as very low dissolved oxygen levels. Mosquitofish give birth to an average of 40-100 live fry, each of which is approximately 3/8" in length. On average, 3 to 4 broods are produced each year, depending on the size of the female and the length of the breeding season. Females can attain a maximum length of two inches; males one inch. Both sexes seldom survive for more than two years.
Throughout its development G. holbrooki has a voracious appetite, feeding on a wide variety of plankton as well as larger aquatic insects. It is a random feeder, with the availability of food being more important than type.
Being opportunistic feeders, other invertebrates and fish fry are readily consumed by G. holbrooki. The mosquitofish has a number of natural enemies including wading birds and various fish such as bass, pickerel and sunfish.
When to Stock
Early spring fish stocking will be most efficient for season-long control. However, mid-season stocking may be appropriate for areas which periodically dry back and re-flood as a result of seasonal weather.
Which Mosquito Species? Which Not?
In general terms. G. holbrooki is attracted to moving, active prey. The feeding and respiratory habits of the various mosquito species will determine Gambusia feeding behavior. For this reason, mosquitofish may not be effective in controlling some Anopheles or Coquillettidia mosquito species. In general, the use and application of G. holbrooki should be by professional mosquito control agencies only. No stocking should take place without first performing an adequate mosquito survey and an investigation of the natural history of each site. All stockings should be made with discrimination, and not randomly.
Habitat Types
Not all bodies of water are suitable for introduction of mosquitofish (lakes, ponds and streams generally are not considered as major sources of mosquito breeding). Some examples of mosquito habitats where fish may be introduced include:
- Stormwater management facilities.
- Ditches and swales.
- Dredge spoil impoundments.
- Artificial containers - i.e., ornamental ponds, abandoned swimming pools and foundations.
- Excavated sites such as farm ponds.
- Sewage lagoons and/or waste-water facilities.
Gambusia should not be stocked in natural wetlands or in areas where threatened or endangered species of fish or amphibians are known to exist. Consult with the County of York, Mosquito Division (890-3790) if there are any questions about the presence of threatened or endangered species.
Gambusia Stocking Rates
| Habitat | Number of fish |
|---|---|
| Bird bath (large) | 10 per site |
| Stormwater Facility | 1,000 per acre |
| Ditches | 1 fish per yard of ditch length |
| Dredge Spoil Impoundments | 2,500 per acre (immediate control) |
| Sewage Lagoons | 1,000 per acre (inoculation rate) |
| Farm Ponds | 1,000 per acre |
