Hasemania is a genus of small tetras (family Characidae) found only in Brazil, mostly in coastal and Atlantic Forest drainages of the country's east. Like many small Brazilian characins, they are slim, schooling fish with a silvery body and — a trait often used to recognize the genus — an adipose fin that is reduced or missing altogether, unusual among characins, where that small fin behind the dorsal is normally present. The atlas's seven species run 1–2 in, tiny stream fish typical of the shaded, tannin-tinted waters common across their Atlantic Forest range.
The genus's best-known aquarium export is Hasemania nana, the silver-tipped tetra, a long-time community-tank staple prized for its coppery body and bright white-tipped fins, undemanding and peaceful in a shoal. Several of its relatives, including H. hanseni and H. maxillaris, carry no established common name and see little to no trade. Conservation status is mixed and, for a Brazil-only genus, concerning: alongside three Least Concern species sits one Critically Endangered and one Endangered species, a pattern consistent with the heavy habitat loss the Atlantic Forest's streams have suffered from agriculture and urban growth.