The wild form is olive green in color, with a red or brown lateral stripe and speckles on the dorsal and, sometimes, caudal fins.

[3] The green swordtail prefers swift-flowing, heavily vegetated rivers and streams, but is also found in warm springs and canals.

The specific name honours the collector of the type, the Austrian botanist Karl Bartholomaeus Heller (1824–1880), who discovered this fish while exploring México in 1845–1848.

[7] X. hellerii is a common laboratory animal and has been used as a model organism in studies involving female mate preference[8] and male conflict.

[10][11][12] Swordtails are some of the easiest fish for amateur aquarist to breed, if the conditions of the tank are appropriate and it contains both males and females reproduction will occur without intervention.

Often all female groups which have come from a mixed gender tank will be pregnant on arrival, creating a breeding population when the fry sexually mature at around three months of age.