Microsternarchus is a genus of small weakly electric knifefishes in the order Gymnotiformes, found in South American river systems in Brazil, Bolivia, Colombia, and Venezuela. The atlas covers 5 species, modest in size for the order at roughly 2–4.5 in, including the Sarapó (Microsternarchus bilineatus) along with Microsternarchus brevis, Microsternarchus javieri, Microsternarchus longicaudatus, and Microsternarchus schonmanni. Like other gymnotiforms, they lack a distinct tail fin, swim primarily by undulating a long anal fin, and generate a continuous weak electric field used for navigation and locating prey in dark or turbid water, a sensory system that has made this whole order a touchstone for neuroscience research into electroreception.
Microsternarchus is little known outside scientific collections and has essentially no presence in the aquarium hobby, unlike some of its more conspicuous knifefish relatives that do reach specialist keepers. Species in this genus are typically nocturnal and secretive, sheltering by day among submerged roots, leaf litter, and marginal vegetation in slow-flowing stretches of Amazon and Orinoco basin habitat, and emerging at night to forage on small invertebrates using electrolocation rather than sight. The atlas lists two species as Least Concern, two Not Evaluated, and one Data Deficient, a spread that reflects how little targeted survey work has been done on the genus rather than any known population decline.
As with other small electric knifefishes, each Microsternarchus species produces a distinct electric organ discharge waveform, a trait researchers use both to distinguish species in the field and to study how electric communication and predator avoidance have evolved within this uniquely South American fish lineage.