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If you mean a large black blotch on the caudal peduncle, this is only seen in A165:
A164 can show a black blotch on the caudal peduncle too, but it is usually smaller, less pronounced and restricted to the area below the lateral band.
After looking at the pictures again, I think it's actually an eunotus-subcomplex species closely related (or identical) to A. sp. Nadelstreifen. Like these fish, A. sp. Nadelstreifen often show prominent vertical bars, but rarely (if ever?) split bars. Caudal spot and coloration of the caudal...
I agree with you Mike that it's likely a regani-complex species, but apart from that, I see no particular similarity to A. paulmuelleri at all. If these fish are in fact frrom Peru, I think that it's an entirely new species. @apistonoob99 do you have any information on the exact catch location?
They are neither iniridae nor D37 but rather a macmasteri-complex species. Which one exactly is impossible to tell for sure from the above pictures. If you have obvious males, show some pictures of them when they have colored up a bit.
Usually the markings should be visible when the fish are displaying (and in females too).
If merely one of your males has ever shown these markings once, I doubt that they are A. sp. Blutkehl.
Some of your fish seem to faintly show the typical black markings in vertical bars 2 & 3 that distinguish D39 from other personata-like species. When shown in a pronounced way, they look like this:
For what do you want to look specifically? That your male is an "Agassizii blue Tefe" is just a guess by some people you have asked. It is impossible to tell this for sure from the looks of your fish - it's just one of many equally probable possibilities. And even if it would be certain that it...
It doesn't look like Netz or BBCS to me.
Since the op mentioned the name "blue Tefe" it might be A. cf. agassizii (Rio Tefe) or it's a domestic strain with that name. In the latter case, it's likely already a mix of different species subsumed under the name "agassizii".
In the first picture I can't see enough relevant features of the fish (e.g. caudal spot, coloration of the dorsal fin) to tell whether it's viejita or not. However, if the caudal spot is shaped like a "D" and the fish doesn't have a red seam at the upper edge of the dorsal, it's not viejita. Imo...
I too think that the first two are not D21. Which macmasteri-subcomplex species it exactly is, is impossible to tell for me. The other fish are for sure not A. uaupesi. They look like D50 to me.