yeah most males will get a nuchal hump but when they are that little it will really only be visible in the most dominant male if even that, and my female has a small hump as well at only 4in so you really have to take all the characteristics together and see which they have more of, my female even had trailers before my male did because he was a late bloomer so all just depends on fish's develop stage, are you trying to get a good male for single specimen or are you trying to breed? if your trying to get a pair i would go ahead and go out and pick up like 2 more (if your tank is big enough of course) that have the dullest body coloring but the most bearding of their gill plates and add them in, as you will get a much stronger bond between the pair and less chance of one killing the other if they are together from a young age