Pacu get far too large for a 90g tank and are mostly herbivores so shouldn't be fed meaty foods like fish on a regular basis.
As for feeders, I would strongly discourage you from feeding any tropical fish feeder goldfish or rosy reds purchased from the store. For one thing, these fish are often kept in very poor conditions and carry lots of diseases as a result. Second, these coldwater species aren't a healthy thing for tropical fish to eat. If you plan on making live feeder fish a major part of your tropical fish's diet, I encourage you to start your own breeding tank for livebearers such as guppies (for smaller fish) or up to mollies (for larger fish).
If you're looking for predatory fish, leopard bushfish would do well in your tank, provided they have plenty of plants. You could house a group of them in tank of that size.