Well, I decided to separate them when they hit about 4" based upon a hobbyist/friend's experience with his. He told me that almost overnight, things can change for the worst. Up to that time they were co-existing quite well. So, just to be on the safe side I split them up. They were in a 90G with a bunch of P. kieneri ... a busy tank which helped suppress aggression, but ultimately too small for them. At some point I'll reintroduce them to one another in a larger tank. In fact, I'll be putting two of them (think they're a pair) into a 180G with a mix of other Madagascans (Ptychochromis, Paratilapia) to see how they fare.
Thanks for the info Jim. They're so strikingly beautiful and yet so incredibly vicious. I always look forward to your updates and hope to see Lamena babies in their future
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