I doubt the fish will much care, but if you want to be somewhat "authentic," here's some data on the natural habitats of this fish. Most commercial fish now are of course tank or farm-raised, and come in a great variety of beautiful colours and varieties.
The natural species (Xiphophorus maculatus) occurs in North and Central America: from Veracruz, Mexico down to Belize, inhabiting creeks and swamps, warm springs, canals and ditches. Typically slow-moving water, with aquatic and marginal vegetation. The species X. variatus was originally endemic to the Atlantic slope of Mexico but introduced or feral populations now exist in several other countries. For both, the aquarium should be well planted and have a minimal flow from the filter. The substrate may be sand or fine gravel, with river rock and/or bogwood. This fish prefers to swim in the middle level of the aquarium.