Originally Posted by aunt kymmie
Same here. I've had mine for two years and she's never grown any bristles. The absence of bristles is the only way to tell the difference between he/she, as far as I know.
The name Bristlenose Plecos has several members of the Genus ancistrus unfortunately, it is like the Common Pleco with last count being around 12 species sold in pet shops under the name Common Pleco and then there are hybrids in most of the Loricoridae Family that aquarists should be informed about..
However I was able to find out a little more about sexual differences and this is species specific but there is other means of sexual identity in some of the species. Which can even include length
Sexual Differences: Most males of the ancistrus species have more and longer tentacles than the females
, this is especially true of the A. hoplygenys.
A. cirrhosis: The male has an antler-like bump on its' forehead while the female has a row of short tentacles.
A. hoplygenys: The male is larger with barbs, the female is smaller without barbs.
A. ranunclus: no info found yet