A single male of the Tequila Splitfin was sampled in 1955 by Miller and Greenbank, but identified erroneously as Zoogoneticus quitzeoensis, with which species it was collected and found sympatrically . Many years later, the mistake was detected, the fish identified as a new species and finally, 43 years after the first capture, described by Webb and Miller.

In 2001, a wild population of this species was rediscovered in a very small spring pool (3 x 4m in diameter). The population there was composed of only a handful of adult fish and a few tens of juveniles (De la Vega-Salazar et al., 2003). In 2007, N. W. Bailey et al showed, that the allelic richness of this population (though it was comparable in size to an aquatic stock) was higher than in any aquatic stock. In 2013 the loss of this population was reported (pers. comm. Domínguez), so there is not much hope that this species is still persisting in the wild.

Restricted to a series of small habitats below the waterfall known as ‘El Salto’ in the upper Río Mezquital basin, Durango state, central Mexico. It was previously considered to occur throughout much of the upper Río Mezquital in both Durango and Coahuila states, but genetic analyses suggest otherwise and have resulted in taxonomic confusion (see ‘Notes’).

Despite often being referred to as extinct in the wild this monotypic species is still surviving at a few localities. It's not particularly scarce in the hobby with strong captive populations existing, some of which have been selectively bred to produce variations in colour and patterning.

As with other goodeids, there is less of a size difference between the sexes than in many other livebearers. This is thought to be related to the relatively primitive…