Additional information (Wiki):

In addition, several species are commonly kept by aquarium hobbyists, especially X. helleri, X. maculatus and X. variatus. In fact, these are a key category in fishkeeping, a group of extremely hardy livebearing fish, along with the molly and guppy, that adapt to almost any water conditions, from cold to tropical, freshwater to fully marine. Unlike many species, these are available almost completely as captive-raised, because of the ease with which they breed.