Ecological Risk Screening Summary - Mexican Molly (Poecilia sphenops) - Uncertain Risk

Species that are considered uncertain risk need a more in-depth assessment beyond the Risk Summary to better define the species’ risk to U.S. environments.

Poecilia sphenops, Mexican Molly, is a poeciliid fish native to Mexico and Central America. This species and its hybrids are common in the aquarium trade, including in the United States. P. sphenops is currently established outside its native range in the United States, Trinidad, Singapore, Hungary, Italy, Japan, and Brazil; the populations in Italy, Japan, and the U.S. State of Montana occur in thermal springs. Taxonomic confusion is common among P. sphenops and closely related species. P. sphenops was reported to negatively affect the Moapa dace (Moapa coriacea) and the White River springfish (Crenichthys baileyi), two endangered species in the United States. However, a later author attributed the effects on M. coriacea and C. baileyi to P. mexicana. Without confirmation that P. sphenops, and not a congener, is negatively affecting the endangered species, the history of invasiveness is “none documented.” P. sphenops has a high climate match with the contiguous United States, with the areas of highest match in the southeastern and southwestern United States. The certainty of assessment is low because of taxonomic uncertainty and the lack of scientifically defensible evidence of negative impacts of introduction. Overall risk assessment category for P. sphenops is “Uncertain.”