Here's a picture of our red bellied pacu, who at the most, sometimes appear have pale salmon colored bellies. As you can see, your fish look like my fish.
The good news about your pacu being red bellies, is that they don't have the potential to grow quite as large as black pacu. However, they can still get up to 36" or longer so will require large tanks that many people can't or are unwilling to provide because of $$$/space limitations.