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I don't think that you can determine which population comes from specific rivers based on minor caudal fin differences alone. There are minor caudal fin pattern differences even within each population of A. agassizii. I can recognize about 4 or 5 forms within the A. agassizii superspecies. Each is isolated regionally, but not by river system alone. Without knowing where the fish was collected I would never attach a population name to it. Based on the 1 photo of a young, not fully developed, male, I would not even try to guess which form it is.
I don't know the collecting place, the only information I have is that the fish was imported from Asia. Maybe when the fish will be adult we can determine the type.
If it came from Asia, then it is a domestic bred specimen. It is impossible to give it a location name because we know nothing about where its ancestors were collected in the wild. For all we know, it could be from a mix of locations or even forms. If I were to describe it, I would call it a domestic red-top/red-tail strain of A. agassizii. I also would not be surprised if the offspring showed several different color morphs. I doubt it is a 'set' strain.