However, the goodeid mating system differs in several ways from the more common livebearing fish from the family Poeciliidae that includes guppies and swordtails.

[3] The redtail splitfin comes from west-central Mexico in the Grande de Santiago River basin and waters near Compostela, Nayarit.

It might also occur in the uppermost Ameca and Armería River basins, but the taxonomic position of these populations remains unclear.

Two additional populations, one from an endorheic basin in the Etzatlán region and another from the Coahuayana River, were formerly included in this species, but in 2016 they were described as X. doadrioi and X. lyonsi respectively.

[4] The redtail splitfin inhabits springs, pools, lakes, creeks and rivers, typically in places with little or no aquatic vegetation.

A broad, poorly defined bluish-black band runs from the gill cover to the tail, but it virtually disappears on the mid-body region.

[7][2] Among goodeids, the distinct red-orange tail and tail-base is unique to the males of the redtail splitfin and its close relatives X. doadrioi and X.