Mosquitofishes (Gambusia)

Fish from the Gambusia genus, also known as mosquitofish or topminnows, are live bearing fishes native to the Americas. Both species that occur in Connecticut, Eastern Mosquitofish (Gambusia holbrooki) and Western Mosquitofish (Gambusia affinis), are introduced. In fact, mosquitofishes have been introduced globally as a biocontrol agent for mosquitoes, given that mosquito larvae comprise part of their diet. However, these introductions have had mixed results at reducing mosquito abundance and mosquitofishes have become established invasive species in many parts of the world where they threaten a number of native fishes and invertebrates.

The two species of mosquitofish in Connecticut are difficult to classify, with some arguing that G. holbrooki is better understood as a subspecies of G. affinis. They are best identified by counting their dorsal rays; however, individual variation and ready hybridization between the species can complicate making a positive identification. An accurate characterization of the true ranges of these species in Connecticut is elusive because they occupy marginal habitats that are rarely sampled by the Fisheries Division and are challenging to identify in the field. 

Select the species' names below to learn more.

Eastern Mosquitofish (Gambusia holbrooki) - Introduced

Western Mosquitofish (Gambusia affinis) - Introduced

Mosquitofish are not commonly kept as aquarium fish due to their aggression and relatively plain appearance.

Content last updated in November 2024.