[3] Gambusia typically eat zooplankton, beetles, mayflies, caddisflies, mites, and other invertebrates; mosquito larvae make up only a small portion of their diet.

[4] Mosquitofish were introduced directly into ecosystems in many parts of the world as a biocontrol[5] to lower mosquito populations which in turn negatively affected many other species in each distinct bioregion.

Several counties in California distribute mosquitofish at no charge to residents with human-made fish ponds and pools as part of their mosquito abatement programs.

On 24 February 2014, Chennai Corporation in India introduced western mosquitofish in 660 ponds to control the mosquito population in freshwater bodies.

[13] Mosquitofish are small and of a dull grey coloring, with a large abdomen, and have rounded dorsal and caudal fins and an upturned mouth.

[19] However, they can suffer mortality if fed only mosquito larvae, and survivors of this diet show poor growth and maturation.

[15] Because of their notable adaptability to harsh conditions and their global introduction into many habitats for mosquito control, they have been described as the most widespread freshwater fish in the world.

[3] However, retrospectively, many introductions could be considered ill-advised; in most cases native fishes supplied control of mosquito populations, and introducing mosquitofish has been harmful to indigenous aquatic life.

[28] However, from the 1920s to the 1950s, mosquitofish were considered by some to be a significant factor in eradicating malaria in South America, southern Russia, and Ukraine.

[31] Through species distribution models, it has been revealed that G. affinis exhibit significant niche expansions beyond their natural climatic ranges, with a notable shift towards tropical regions in Asia.

[5] These findings highlight the ecological flexibility of these species, contributing to their extensive success and posing a substantial risk for further range expansion.

[5] Reproduction of the mosquitofish starts with the male arranging the rays of the gonopodium (modified anal fin) into a slight tube.

The male mosquitofish uses this tubular fin to secrete milt into the female's genital aperture in the process of internal fertilization.

[3][11][2] The female's genital aperture is located just behind the anal fin and is an opening for the milt to fertilize the ova within the ovary.

[35] If the gestation period is shorter, each newborn will at birth still have a yolk sac connected through a slit located on the ventral side of the body wall.

Growth rates of juvenile mosquitofish reach their peak when the water temperature is within a range of 24 to 30 °C (75 to 86 °F), depending on resource availability.