if you're thinking of putting multiple species of Hoplias together, that will likley end in tears. Most attempts at Hoplias Sp. Co-habs end in trouble with exception to Intermedius. If they pair off, you'll have a much better chance but that will make adding anything else very risky. My Hoplerythrinus - Hoplias co-hab works 90% of the time but my Curupira is unpredictable. One day he can be sedate, the next he can be chasing the Cichla or Brycon. The Hoplerythrinus stay very clear of him most of the time.
The golds are very active and rarely sit still for much time. They don't claim territory either, or at least, not in the same way Hoplias or Cichlids do. In that sense, they are more like Brycon as they patrol, occasionally stopping for a break or a gasp of air. If you put them into a small tank, you'll loose this behaviour and they become much less active, sitting on the substrate, occasionally breaking for a gasp of air. They do not seek out cover, not that I've ever seen anyway. They will hang in the outflow of my filters, swimming aganist the current but generally prefer the slower water.
