First record of the Twospot Livebearer, Pseudoxiphophorus bimaculatus (Heckel, 1848) (Poeciliidae), a non-native fish in an endorheic sub-basin of the highlands of Chiapas, Mexico

From November 2025 to March 2026, we recorded the presence of the Twospot Livebearer, Pseudoxiphophorus bimaculatus (Heckel, 1848), as a non-native species in the Amarillo River sub-basin, Chiapas, Mexico.  Specimens were found at 2,113 m above sea level in a drainage ditch connecting an artificial lagoon to an urbanized river in the municipality of San Cristóbal de Las Casas. We collected 327 individuals with standard lengths of 7–38 mm. The presence of multiple size classes, including juvenile specimens, indicates the establishment of a breeding population. This non-native species directly threatens the endemic, endangered Chiapas Killifish, Tlaloc hildebrandi (Miller, 1950).