Yes I agree with you it is pretty hard to sex Peps. However, I've been buying 10 - 15 peppermint fry every six months for the last 6 years I've been breeding and do sell off the obvious males. I then continue to sell off the fish that develop into males.
Further, I've been selling my fish collection off and generally my fish are larger than what I've advertised them for. The last breeding pair I sold was actually a few CM's larger. I do this because I don't want to catch the fish and measure them and I usually advise the buyer prior to them agreeing to purchase the fish.
Now, I personally believe these fish are female because at the size of 5.5 - 7.00cm they have only a few bristles on their nose. All my sub-dominant males grew plenty of bristles at a much younger age.
Finally, I will sincerely appreciate it if you don't ever give your opinion about what I'm selling for the following reason;
1) Your post has destroyed this sale. (by putting doubt in prospective buyers minds) I'm probably the most honest and generous person on this forum. I never sell fish unless I show the buyers what they're getting and I gave away a lot of free fish and caves in the last sales I've made.
2) Only a fool would believe that a fish at 7.5cm (I'm being conservative with the measurement) with only two bristles on the front of its nose will become a male.
3) The other fish at 5.5cm (I'm only being conservative with the measurement) also only have 2 or three bristles on their nose.
4) From my experience, if a fish has two – four bristles on the it's lip's, at the size I'm advertising, it has always been a female fish. The second a bristle grows around the lips I will always off load it as I didn't need male fish.
