It's a bit confusing at first... but that fish is a Serrasalmus Spilopleura. Spilos that are gold, are normally called Serrasalmus Maculatus, and their red Spilos that are reddish are called Ruby Red Spilos.
So that's why you may hear people refer to that fish as a "Gold Mac" or "Maculatus" or "Gold Spilo" or "Spilo"...
To avoid confusion, just call it a Mac (Maculatus).