IDK the dimensions so I'll speak on the volume alone. Also, I trust you know the basics of the stocking, at the very least a cubic inch of fish per gallon rule of thumb, and are an experienced aquarist.
IMHO, TSN you can keep in 1600 gal because they are all runts, dinks, and other kinds of underachievers. That's 99.99% of what we have available in this great hobby of ours. It's overrun with millions of TSN culls - refuse from food fish farms that offers unbeatable profitability.
So, expecting your runt TSN not to exceed 24"-30" even after 5-10 years, you could do quite a few of them in there -
wednesday13
kept over a dozen or maybe two dozen in 1700 gal pond in his basement but your filtration, water turnover, water change, and aeration must be appropriately sized or oversized. It'd be nice IME and IMO to have a sump that's at least half or the same size as your large tank. This sump will also help you out tremendously in case you need an emergency water change by serving as a reservoir.
Black Pacu grow huge, up to 25-40 lbs. You probably can keep a few in there but it will cramp everything else up. If you are prepared to have them as your center pieces, it could be done. They are pigs though, food hoarders and are nasty to timid or even simply placid tank mates - they will start biting their fins off and barbels too sooner or later. For instance, I found I cannot keep iridescent shark catfish and channel catfish with pacu. Pacu will supplement their diet non-stop on these catfishes' fins and barbels.
A community would be nice. Still, I'd encourage you to ponder a solo fish exhibit, or some such. It's a bit too tight for an adult wels catfish but could be ok for a Wallago leerii, or a Nile Perch, perhaps African tigerfish, several temensis pbass (see below), etc. In that vein.
An example of not many but very highly impressive fish:
, so im not so sure about them.
.
thebiggerthebetter
and the rest of the guys in the catfish sub forum would know better than I.
