His info don't believe applies to bolivian the same as German. I'm in the same boat just brought home 4 bolivian and it's almost impossible to tell the difference.. I would suggest give no them a few days to acclimate and then try to judge the dorsal fins, and "anal spur" the males will generally have the second Spike on their dorsal fin be longer, and the anal spur will be smaller and point back, where as the female will be bigger, rounder and point down more.. Of course this is just what I've read and it's harder to judge in practice.How long have you had them? They look like new additions since they have not fully colored up yet, or maybe its because you got the pictures shortly after the tank lights came on. A good rule of thumb is that male GBR's will not have any blue speckling inside the black spots on their sides, as to where females will, also females will have a pinker underbelly than males, here are a couple of pictures that point out a few differences between the two.
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Yeah, these are Bolivians, not GBRs. I'll try to get better pics. I got them about two weeks ago.