The mosquitofish, Gambusia affinis (Baird & Girard, 1853), is a species of freshwater fish. It is a member of the family Poeciliidae of order Cyprinodontiformes.

These fish are native to the watershed of the Gulf of Mexico, where it has long been known that they feed readily on the aquatic larval and pupal stages of mosquitoes. They are remarkably hardy, surviving in waters of very low oxygen saturations, high salinities (including twice that of seawater), and high temperatures; they can even survive in waters up to 42 °C for short periods. For these reasons, this species may now be the most widespread freshwater fish in the world, having been introduced as a biocontrol to tropical and temperate countries in both hemispheres, and then spreading further both naturally and through even further introductions.

The mosquitofish is a small and stout, dull grey, robust fish with a rounded tail and a terminal and upward-pointing mouth adapted for feeding at the water's surface. In these features and their small size they resemble the tropical guppies, which belong to the same taxonomic family. Sexual dimorphism is pronounced; mature females reach a maximum overall length of 7 cm, while males reach only 4 cm.

Females can reach sexual maturity in only six to eight weeks, and they may bear three to four broods of young in a single season. The first may number only a dozen, but later broods include 60 to 100 young. Females store sperm in their reproductive tract for up to two months and give birth to live offspring. Live-bearing gives their young a much higher survival rate than in most species of egg-laying fish, which typically suffer from egg predation.

Under favourable conditions, mosquitofish live two to three years. Estimates of their breeding potential have therefore demonstrated an incredible ability for this species to multiply and dominate new habitats into which they have been introduced. Their success in a new environment is almost guaranteed by their rapid maturation, by breeding several times a year, and producing broods of around 50 advanced live young. Individual populations have been recorded expanding from 7,000 to 120,000 in five months.

The mosquitofish is also commonly known simply by its generic name, Gambusia, although such usage is, to say the least, ambiguous. It is sometimes called the western mosquitofish, to distinguish it from the eastern mosquitofish (G. holbrooki). At least in Hong Kong, it is also known as the live-bearing tooth-carp.

References

• FishBase: Gambusia affinis
• ITIS: Gambusia affinis

External links

• Gambusia Control Homepage