Plesiolebias is a genus of South American annual killifish restricted to Brazil, part of the seasonal-pool lineage that also includes Cynolebias and its many relatives. Atlas species are among the smallest killifish in the atlas, spanning just 0.5–2 in, and follow the classic annual-killifish life history: adults live in shallow, temporary pools that form with seasonal rains, and before the water dries up they bury eggs in the mud substrate, where embryos enter a diapause and wait out the dry season until the next rains hatch them.
This is a genus of specialist rather than mainstream aquarium interest - annual killifish keepers who work with peat-based substrate spawning and dry-storage incubation are the main audience for a genus this small and this tied to Brazil's temporary wetlands, and individual Plesiolebias species are rarely seen outside dedicated killifish circles. Conservation status is reassuring for now - five of the six atlas species are assessed Least Concern, with one Endangered - though as with other temporary-pool killifish, that status can shift quickly if the specific wetlands a species depends on are drained or developed.