Black Neon Tetra ---- Hyphessobrycon herbertaxelrodi.. The black neon tetra (Hyphessobrycon herbertaxelrodi) is a freshwater fish of the characin family (family Characidae) of order Characiformes. It is native to the Paraguay basin of southern Brazil. Black neon tetras should be kept in soft acidic water, which should be kept clean at all times. Their tank should contain live plants, a darker substrate and open water for swimming. Black neons should be kept in groups of at least 4−6.