Just a quick update... I'm totally baffled by this male notatus. He has now completely ousted the female Atabapo and is guarding the fry on his own. The male Atabapo is still defending the territory, and every time he comes back around from chasing away a fish, he briefly and half-heartedly attacks the notatus. I think he's just confused as to why another fish is guarding his fry. The major aggression has stopped and the female Atabapo has joined the rest of her tankmates on the opposite side of the tank. The notatus is still in parenting colors -- black body and bright eyes -- and is constantly twitching and signaling the fry. The fry don't seem confused at all. They seem to recognize him as their parent. Of course, he's not mouthbrooding, so they just huddle around him when they feel threatened.