Melanorivulus is a genus of small killifish in the family Rivulidae, split out of the old catch-all genus Rivulus as that group was revised along South American lines. The atlas's 15 species come from Brazil, Bolivia, Guyana, Paraguay, Suriname, and Venezuela, mostly from the savanna and cerrado drainages of central South America, where they live in shallow forest-edge pools, seasonal wetlands, and slow backwaters rather than open river channels. Many rivulids in this part of the family tree are associated with temporary or semi-temporary water that can shrink or dry between rainy seasons, and their eggs are adapted to tolerate a dry spell buried in the substrate, though not every Melanorivulus species is a strict annual fish, so habitat permanence varies by locality.
None of the 15 Melanorivulus species covered here have an established common name, and the genus sits well outside the mainstream aquarium trade, kept mostly by killifish specialists who prize the group for its understated but often richly patterned males rather than for flashy color. Care follows general small-killifish practice: soft, acidic, well-planted water, a peat or leaf-litter substrate for species that need one, and small live or frozen foods. The IUCN picture is mixed, with several species assessed as Least Concern but three as Vulnerable and a handful still unassessed, consistent with a genus of small, range-restricted fish scattered across seasonal habitat that is easy to overlook and, in places, easy to drain or convert to pasture.