Helene, I am an admirer of your new photos, too!
And it surely is a task of some importance to photograph females and young growing fish. Of course, the females of many bintan-variants differ only slightly, but to compare the females of prnaticauda, parvulus, filamentosus, nagyi, harveyi, allani, opallios, deissneri, tweeidiei or phoenicurus and even of some non-described forms as spec. Ampah or spec. Sungai Stunggang maybe highly informative. In fact, we surely must supply some colour features into some of the descriptions, but that should be assisted by good photos of females.
Another interesting question is: At what age could one distinguish sex in growing young? THis should be assited by good photos, too.