You could easily keep 5 or 6 in a 40 gallon vivarium, and have a pretty good chance for getting both males and females. Just a hint, in case your choice of auratus proves shy--They appear to feel more secure in a rather heavily planted tank, and you're likely to see more of them than you may with more sparse cover.
-----
Patty
Pahsimeroi, Idaho

D. auratus blue, auratus Ancon Hill, galactonotus orange, galactonotus yellow, fantasticus, reticulatus, imitator, castaneoticus, azureus, pumilio Bastimentos. P. lugubris, vittatus, terribilis mint green, terribilis orange.