Ecological Risk Screening Summary - Western Mosquitofish (Gambusia affinis) - High Risk

Species that are considered high risk have a well-documented history of invasiveness in at least one location globally, and a high or medium climate match to the contiguous United States.

Gambusia affinis, the western mosquitofish, is a fish native to the Mississippi River basin from central Indiana and Illinois, south to the Gulf of Mexico, and the Gulf Slope drainages west to Mexico. Gambusia affinis has been routinely introduced and stocked around the world for mosquito control. The species has also been reported as an import for research or aquaria. The life history of Gambusia affinis is flexible. The fish is an opportunistic omnivore, viviparous, and has a strong dispersal tendency. The History of Invasiveness for Gambusia affinis is classified as High. Well documented nonnative introductions have led to established populations with negative impacts to native species and environments through predation and competition. The climate matching analysis for the contiguous United States indicates establishment concern for this species outside its native range. The entirety of the contiguous United States had a high climate match for G. affinis. The Certainty of Assessment for this ERSS is classified as High due to the wide availability of reliable information regarding Gambusia affinis. The Overall Risk Assessment Category for Gambusia affinis in the contiguous United States is High.