Phenacogaster is a genus of small characin fishes, often called glass tetras for their thin, partly translucent bodies, in the family Characidae, native to river drainages across northern and central South America: Brazil, Colombia, Venezuela, Guyana, Bolivia, Paraguay, Argentina, and French Guiana, per the atlas's coverage. They are slim, silvery fish, generally under 2.5 in, typical of small characins that shoal in slow water and leaf litter along stream margins. The atlas covers 25 species.
Phenacogaster has almost no presence in the aquarium trade compared with showier tetra genera, and most species, including the large stain-glass tetra (P. megalostictus) and six-eyed tetra (P. tegatus), are known mainly from museum collections and regional ichthyological surveys rather than hobbyist tanks. The great majority of species in the genus have not been formally assessed for conservation status, so, as with many small, plainly patterned South American characins, the honest picture is one of insufficient data rather than confirmed safety.