Empetrichthys, the poolfishes, are small desert fish confined to isolated spring and pool systems in the southwestern United States. Long treated as close relatives of the livebearing goodeids, they are themselves egg-layers, part of a lineage of relict cyprinodontiform fish stranded in fragments of a once much wetter Pleistocene landscape. The atlas covers the genus's 2 species, both native only to the United States, running roughly 2.5–3.5 in, with a compact body and blunt head typical of small spring-dwelling toothcarps.
Neither species has any real place in the aquarium hobby - both are legally protected, geographically inaccessible endemics rather than trade fish. The Ash Meadows poolfish (Empetrichthys merriami) is now Extinct, lost after its Nevada spring habitat was pumped dry and altered in the mid-20th century. The Pahrump poolfish (Empetrichthys latos) survives only in introduced refuge populations after its original spring dried up, and is listed Critically Endangered - one of the starkest illustrations in the atlas of how narrow a desert fish's entire world can be.