Great advice so far from Duane and Laurie!
Old World owned by Laif de Maison (in Florida) farms kieneri and most of the Madagascar fish that are available. He presented for CCA a couple of years ago about - among other things - bringing back his farm after a bad hurricane. To my knowledge, they're the only place farming them (and a bunch of other really rare Africans), so another bad Hurricane (or cold snap or mishap or whatever) and it's lights out for the availability of these guys outside of hobbyists (which is why it's great to see some folks keeping and breeding them).
I got a group of 6 x Kieneri from Dave's Rare Fish (
www.davesfish.com) a few years ago at 1.5" or so and grew them out in a 4' tank. They grew to ~4" quickly and then growth slowed. They would have been better in a 6' tank but I thought I could get away with it because they're a smaller species. Ultimately, I lost a couple (and both of my female P. dambabe) in a 6-day power outage and I think the rest when something else in the tank bred (I don't recall). Definitely an interesting fish and more manageable than the larger Paretroplus. Mine could be rough on each other but were pretty much ignored by other fish (except during breeding)...
P. menarembo are a whole different league of fish. They easily grow to a foot+ and also need to be in groups. I've tried a couple of big Paretroplus in pairs or trios and it didn't work well. My P. maculatus get big but don't spawn and (before they died during the power outage) the P. dambabe would chase the females (and similar shape fish like severums) pretty much all day.
I'd keep Paretroplus in two different 150g tanks: One giant male P. dambabe with three Royal Plecos and a bunch of driftwood and (different tank) a large male maculatus with a group of Astatheros rostratus, nicaraguense and some acaras.
Matt