To me they are still looking to young/ small to accurately sex. I have had some of my young males start developing bristles around the 8cm mark, but I had to look pretty closely - the bristles were very short and stumpy at that size. It's been a while now since my breeders started breeding but I believe that the male was around 12cm and the female was around 10cm. Mind you this is just that particular pair and other people may have had them breed at a smaller size, personally I wouldn't try breeding them to young simply because it will put a lot of physical strain on a small male to try can care for eggs and newly born babies and a small female will most likely not produce a great deal of eggs anyway. So for the time being enjoy the BN's in their youthful activities because I can almost gaurentee that as they get bigger and especailly if they are a pair and breed then you'll be going "Bristle Nose what Bristle Nose?", and will just see a portion of tail or fin sticking out of their favourite hidey hole. Or see them when you drop in a treat to eat, or even more annoyingly see a flash of them as they disappear just as either the fish light or room light comes on.
