The black phantom tetra (Hyphessobrycon megalopterus) is a freshwater fish of the characin family (family Characidae) of order Characiformes. It is native to the Paraguay, Guaporé, and Mamore basins in Brazil and Bolivia.
This fish is of roughly tetragonal shape, light grey in coloring, with a black patch, surrounded by iridescent silver edging, posterior of the gills on each side. The male's fins are black, as is the female's dorsal fin; the female's pelvic, anal, and adipose fins are reddish in color. A long-finned variety, apparently developed by captive breeders, is sometimes sold (the male has elongated dorsal and anal fins even in the wild form). The black phantom tetra reaches a maximum overall length of approximately 4.5 cm (1.75 in).
H. megalopterus is one of the more popular tetras sold in the aquarium trade. While it is not particularly colorful, it makes up for this by its display behavior: the males are territorial and defend their space against their neighbors by presenting themselves in profile with the dorsal and anal fins fully extended, and the dark color intensified, making the edging of the body patch stand out prominently. Sometimes they exchange blows which can tear the fins, but this damage heals quickly. Unlike other tetra who prefer to live in large swarms, they will also do fine when kept in a group of 4 or 5 individuals, making them suitable for smaller aquaria. There should still be enough space for the males to stake territories and present themselves to best effort, however.
Megalomphodus megalopterus and Megalamphodus rogoaguae are obsolete synonyms for this species.