Girardinus is a genus of livebearers (family Poeciliidae) endemic to Cuba, where all six atlas species are found. Like other poeciliids, males fertilize females internally via a modified anal fin, the gonopodium, and females give birth to free-swimming young rather than laying eggs. Atlas species run a modest 3–3.5 in, with the sexual dimorphism typical of poeciliids: smaller, more colorful, more elaborately finned males and larger, plainer females.
G. metallicus, the metallic livebearer, is the species with the longest aquarium history, a hardy schooling fish suited to a community setup much like the better-known Poecilia and Xiphophorus livebearers, though the genus as a whole is seen far less often in the trade than those more familiar Cuban and Central American relatives. Conservation status is a bright spot here: all six atlas species are rated Least Concern, and none is flagged under the CARES program, a comparatively rare clean bill of health among the genus hubs this atlas covers.