Yellow swordtail
The yellow swordtail is a species of freshwater fish in the family Poeciliidae. It is endemic to the upper Coatzacoalcos River basin in southern Mexico. It is typically found in brooks and streams with slow current; it is less frequent in areas with strong current. The yellow swordtail is considered a threatened species by Mexican authorities. It reaches up to in standard length.
Unusually, the yellow swordtail appears to be the result of hybrid speciation, and its ancestors a platy species and a swordtail species. The southern mountain swordtail, which is found further south in the Coatzacoalcos River basin than the yellow swordtail, is the result of a similar event.
