Rosy Tetra

Rosy Tetra (Megalamphodus rosaceus) is a species of fish in the family Acestrorhamphidae. It is native to South America (Guianas and lower Amazon). The rosy tetra is kept for the male's dorsal fin. Mature males carry it long and flowing, along with an extended anal fin, and they are the larger, slimmer and more colourful sex — which is unusual enough among tetras to be most of the reason people buy the species. It reaches about 4 cm and comes from the Essequibo, Corantijn and Suriname drainages of Guyana, Suriname and Brazil, in sluggish forest tributaries off the main channels, where decaying leaf litter stains the water and drives the pH down. It colours best in exactly those conditions: acidic water, dim light, driftwood and leaves. It was once treated as a subspecies of Hyphessobrycon bentosi, which it is still regularly confused with; the absence of a dark mark behind the gill cover separates the two.