Markiana is a genus of comparatively large tetras (family Characidae) widespread across South American lowland river systems, with the atlas recording it from Argentina, Bolivia, Brazil, Paraguay, and Venezuela — spanning the Paraguay-Parana and Orinoco drainages. Atlas species are large by tetra standards, 10 to nearly 5 in as adults, with a deep, laterally compressed, silvery body built for open water rather than dense cover. The genus draws scientific interest partly from that size and shape, which sets it apart from the small schooling tetras most aquarists associate with the family.
The sailfin tetra, Markiana nigripinnis, is the species aquarists are likely to encounter — named for its tall, sail-like dorsal fin, it is a hardy, active schooling fish for larger community tanks, best kept in a decent-sized group given both its size and boisterous swimming. M. geayi, from the Orinoco basin, is far less documented in the hobby. Conservation status is only partly resolved: M. nigripinnis is Least Concern, while M. geayi has not been evaluated, leaving its population status effectively unknown.