Hemigrammus filamentosus is a relatively recently described species of tetra from the Rio Araguaia in Brazil. Not quite reaching 2", these are a nice compact tetra with a great attitude. While a standard silver tetra as far as body colour is concerned, the males are quite something; their fins are metallic red, and they develop beautiful, threadlike fin extensions with maturity.
This is a captive bred batch of adults, around 1.5" long. While a couple males have started to colour up, they still need some conditioning to reach their full potential.