About twenty years ago the legend Rosario LaCorte discovered this species in an import. He acquired these, bred them, and distributed them into the hobby.  The species has yet to be described, but it is has acquired the designation of 'Sunset'.  Males (shown in the photo) have elongated fins and more yellow and markings than the females.  Sexual dimorphism is easy to observe when they are adults.  I kept my males and females isolated from each other and they reliable spawned within a couple of days of each of my 'pair' spawning attempts.  I obtained 20-40 fry for each spawn. 

Currently, Wet Spot is selling them for $39 each: https://www.wetspottropicalfish.com/product/hyphessobrycon-sp-4/ 

The photo is of the adults used in my multiple spawning set-ups.  The bag will contain emerging young adults.  The adults came from Stephan Tanner (Amazonas) who is connected with importers and specialists.